KR101948263B1 - Morphology-induced solvatochromic hybrid carbon nanosheets - Google Patents

Abstract

The present invention relates to a solvent-discolorable hybrid carbon nanosheet and a method for producing the hybrid carbon nanosheet, and more particularly, to a hybrid carbon nanosheet having a carbon nanorning formed on the surface of a graphene oxide nanosheet by hydrothermally carbonizing a low molecular weight precursor in the presence of a graphene oxide nanosheet. A sheet may be provided, and the hybrid carbon nanosheets can emit a very wide variety of colors under UV and visible light irradiation depending on the polarity of the solvent.

Description

MORPHOLOGY-INDUCED SOLVATOCHROMIC HYBRID CARBON NANOSHEETS < RTI ID = 0.0 >

TECHNICAL FIELD The present invention relates to a carbon nanomaterial having photoluminescence characteristics, and more particularly, to a solvent-discoloring hybrid carbon nanosheet and a method for producing the same.

Photoluminescent carbon nanomaterials are attracting attention due to their excellent optical properties and optical stability, and they are usefully used in optoelectronic devices, biological labels, sensors, and the like. It has been known that the photoluminescence characteristics of carbon nanomaterials vary depending on the crystal structure, dimensions and chemical functionalization of carbon nanomaterials (Sun, YP et al., J. Am. Chem. Soc . 128, 7756-7757 (2006)). However, the conventional carbon nanomaterial has a limited application field because it emits light in a narrow color range due to blue light emission of a relatively low quantum yield (QY).

There have been attempts to improve the photoluminescence properties of carbon nanomaterials by methods such as synthesis control using various precursors, surface protection, heteroatom doping, chemical reduction, and chromatographic separation after synthesis. In addition to the above-mentioned synthesis method, a solvatochromism phenomenon in which the luminous spectrum of the luminophore is controlled by changing the polarity of the solvent, for example, is used.

As is often found in organic dyes, the electron transition energy can cause solvation through interaction between solute-solvent, and as a result can shift the absorption spectrum and the photoluminescence spectrum. BACKGROUND ART Recently, carbon nanomaterials such as carbon nanotubes, graphene oxide (GO), and carbon nanotubes (CD) have been used as a surface trap state, which depends on a preferential interaction with a solvent molecule or solvent polarity ) Is known to change the light emission.

However, in spite of various studies on carbon nanomaterials which exhibit conventional solvent-dependent photoluminescence, it has not been possible to display all the colors in various ways.

On the other hand, oxidized graphene has been used to modify the molecular structure of carbon nanomaterials due to its surface functional groups and wide specific surface area. For example, oxidized graphene can change the spherical shape of glucose carbonized by a hydrothermal reaction into a two-dimensional structure.

 Sun, Y. P. et al. Quantum-Sized Carbon Dots for Bright and Colorful Photoluminescence. J. Am. Chem. Soc. 128, 7756-7757 (2006)

An object of the present invention is to provide a hybrid carbon nanosheet which can be changed into a very wide variety of colors under UV and visible light depending on a solvent, its application to various fields, a method capable of producing the same in a simple manner, It is a reversible and reproducible method of emitting light.

According to the above object, the present invention provides a graft oxide nanosheet; And carbon nanoring formed on the graphene oxide nanosheet. The present invention also provides a hybrid carbon nanosheet.

The present invention also provides optoelectronic devices, biological labels and sensors comprising the hybrid carbon nanosheets.

The present invention also provides a method for producing a nanocrystalline oxide film, comprising the steps of: (1) preparing a dispersion solution of graft oxide nanosheet; (2) adding a low molecular precursor including an organic acid and an amine compound to the dispersion solution to obtain a mixed dispersion solution; And (3) subjecting the mixed dispersion solution to hydrothermal carbonization. The present invention also provides a method for producing a hybrid carbon nanosheet.

The present invention also relates to the hybrid carbon nanosheet; And organic solvents such as water, ethylene glycol, methanol, ethylene glycol monomethyl ether, ethanol, n-butanol, isopropanol, acrylonitrile, dimethyl sulfoxide, dimethyl formamide, N- And at least one solvent selected from the group consisting of hydrofluoric acid, hydrofluoric acid, and hydrofluoric acid.

The present invention also provides a method for producing a carbon nanostructure, comprising: (1) preparing a first solution by adding a hybrid carbon nanosheet to a first solvent; And (2) illuminating the first solution with excitation light to emit a first hue.

According to the present invention, a novel solvent-discolored hybrid carbon nanosheet having a cluster of carbon nanorings formed on the surface of a graphene oxide nanosheet by hydrothermalizing a low-molecular precursor in the presence of an oxidized graphene nanosheet can be provided.

The hybrid carbon nanosheets may vary in a wide variety of colors under UV and visible light irradiation depending on the polarity of the solvent.

Such a solvent discoloration property is caused by a shape variation in which the two-dimensional carbon nanosheets are three-dimensionally wrinkled by the hydrogen bonding interaction between the carbon nanosheets and the solvent.

Therefore, the novel carbon nanostructure can open new possibilities using the photophysical properties of carbon nanomaterials.

Hereinafter, the present invention will be described in more detail with reference to the drawings.
The meanings of the abbreviations used in the following are described in detail for the purpose of carrying out the invention.
FIG. 1 (a) is a schematic diagram showing a method of synthesizing a hybrid carbon nanosheet (CNS), and FIG. 1 (b) is a schematic diagram showing a method of synthesizing an optical image when the CNS dispersion is excited with 365 nm light in a different solvent (concentration 0.10 mg / to be.
2 (a) to 2 (c) are UV / Vis and photoluminescence spectra of CNS in water, EtOH and DMF, respectively, at 430 nm, 590 nm (water), 575 nm (EtOH) and 550 nm (DMF), (f) shows normalized PL decay (CNS) spectra in three representative solvents observed at 590 nm (water), 575 nm (EtOH) and 550 nm profiles.
Figures 3 (a) and 3 (b) are TEM images of CNS in water, (c) and (d) are TEM images of CNS in DMF, (e) D _h ) as a volume average fraction measured by DLS.
4 (a) is a graph showing the Stokes shift of the photoluminescence band excited at 480 nm according to the change of solvent polarity (E _T (30)) and acidity (Kamlet-Taft acidity,?) (b) is a schematic diagram of the changed shape of the CNS in polar and nonpolar solvents, (c) is the energy diagram of the CNS according to the solvent, and (d) is the energy diagram obtained from solvents of different polarities at 360 nm and 480 nm (1: THF, 2: acetone, 3: NMP, 4: DMF, 5: DMSO, 6: ACN, 7: IPA, 8: n-BuOH, 9: EtOH , 10: EGME, 11: MeOH, 12: EG, 13: water).
5 (a) to 5 (e) are UV / Vis and photoluminescence spectra of CNS measured in EG, MeOH, EGME, n-BuOH and IPA, respectively.
6 (a) to 6 (e) are UV / Vis and photoluminescence spectra of CNS measured in MeCN, DMSO, NMP, acetone and THF, respectively.
7 (a) is an optical image of CNS observed in a mixed solvent of water and DMF at a ratio of 10: 0, 7: 3, 5: 5, 3: 7 and 0:10, (C) is a two-dimensional photoluminescence spectrum of the CNS.
Figure 8 is TEM image (top) and DLS histogram (bottom) of CNS in ethanol, IPA and DMSO.
Figures 9 (a) and 9 (b) are TEM images and optical images observed when the solvent was changed from water to DMF and from DMF to water, respectively.
10 (a) to 10 (c) are TEM images and optical images of carbon nanorings synthesized from small molecules without graft oxide (GO) nanosheets, and FIGS. 10 (d) , Ethanol and DMF.
Figure 11 is the FT-IR spectrum of CNS-water and CNS-DMF.
Figures 12 (a) - (c) are deconvoluted high resolution C1s XPS spectra of CNS-water, CNS-EtOH and CNS-DMF, respectively.
Figure 13 shows the stokes shift for the solvent polarity factors Kamlet-Taft factors ([beta] and [pi] *).

Hereinafter, the present invention will be described more specifically.

The present invention relates to an oxide graphene nanosheet; And a carbon nanorring formed on the graphene oxide nanosheet. The present invention also provides a hybrid carbon nanosheet.

The graphene oxide nanosheet acts as a support in the hybrid carbon nanosheet of the present invention.

The graphene oxide nanosheets can be prepared by conventional methods. For example, the graphene oxide nanosheets can be prepared by a Hummer method or by a slightly modified method thereof.

The graft oxide nanosheets may have various functional groups on the surface. For example, the graphene oxide nanosheet may have an oxygen-containing functional group on its surface. As a specific example, the graphene oxide nanosheet may have a carboxyl group (-COOH), an oxo group (-C═O), or the like on its surface.

The carbon nanorings are nanomaterials having a carbon structure in the ring form.

The carbon nanorings are formed on the graphene oxide nanosheets, and act as chromophores in the hybrid carbon nanosheets.

The carbon nanorings may be formed by hydrothermal carbonization of a low-molecular precursor.

The low molecular weight precursor may include at least one compound having a molecular weight of 30 to 1000 g / mol or 50 to 500 g / mol.

The low molecular weight precursor may include an organic acid. The organic acid may comprise citric acid. Further, the low molecular weight precursor may include an amine compound, and thus the carbon nanorings may be doped with nitrogen (N). Further, the low molecular precursor may include boric acid, and thus the carbon nanorings may be doped with boron (B). As a specific example, the low molecular weight precursor may include an organic acid, an amine compound, and boric acid.

Conventionally, it is known to carbonize a low molecular precursor with a microwave or the like without a separate support or frame to obtain spherical carbon nano dots. However, according to the present invention, a low molecular precursor is carbonized by hydrothermal reaction in the presence of an oxidized graphene nanosheet, The carbon nanorings can be formed on the graphene nanosheet.

The carbon nanorings mainly contain a carbon component and an oxygen component. Specifically, the carbon nanorings may contain 20 to 70% elemental carbon and 20 to 60% elemental oxygen. More specifically, it may contain 35 to 43% by atom of carbon component and 38 to 46% by atom of oxygen component.

The carbon nanorings may be doped with nitrogen. That is, the carbon nanorings may contain a nitrogen component. Specifically, the carbon nanorings may contain a nitrogen component in an amount of 10 to 30%, more specifically 11 to 13%.

Further, the carbon nanorings may be doped with boron. That is, the carbon nanorings may further contain a boron component. Specifically, the carbon nanorings may contain a boron component in an amount of more than 0 to 10%, more specifically more than 0 and 3.5%.

Further, the carbon nanorings may be doped with nitrogen and boron. That is, the carbon nanorings may further contain nitrogen and a boron component. At this time, the contents of nitrogen and boron may be as described above.

The carbon nano ring may have a carbon number (C / N) of 2 to 6 carbon atoms with respect to the nitrogen component, and specifically, a carbon number of 4 to 5 carbon atoms with respect to the nitrogen component.

The carbon nanorings may have at least one group selected from the group consisting of carbonyl group, carboxyl group, B-OH, pyrrolic-N, and graphitic N.

The carbon nanorings may comprise at least 60 weight percent graphitic N based on the total weight of doped nitrogen. Specifically, it may comprise 60 to 70% by weight of graphitic N based on the total weight of doped nitrogen. More specifically, it may comprise 63 to 69 wt% graphitic N based on the total weight of doped nitrogen.

The carbon nanorings may have a diameter of 5 to 50 nm, more specifically, a diameter of 10 to 20 nm.

In addition, the carbon nanorings may have an interlayer spacing of 0.30 to 0.40 nm, and more specifically, an interlayer distance of 0.340 to 0.349 nm.

Further, the carbon nano-rings may be formed of the graphene oxide unit of the nano-sheet area (㎛ ²⁾ 180 per / ㎛ ² or more, 200 / ㎛ ² or more, or 180-230 / ㎛ ^2.

The carbon nanorings can be obtained by hydrothermally carbonizing a low molecular weight precursor. In the present invention, carbon nanorings can be formed on a graft oxide nanosheet by hydrothermally carbonizing a low molecular weight precursor in the presence of an oxidized graphene nanosheet. That is, the hybrid carbon nanosheets can be obtained by hydrothermally carbonizing a low molecular weight precursor in the presence of an oxidized graphene nanosheet.

The hybrid carbon nanosheets have a morphology-induced solvatochromism through shape change. Specifically, when the hybrid carbon nanosheets are present in the solvent, the shape and the luminescent color may change depending on the polarity of the solvent.

The graft oxide nanosheets constituting the hybrid carbon nanosheets are excellent in dispersibility in solvents such as water, ethanol and DMF, but the carbon nanorings have poor dispersibility in solvents other than water. The hybrid carbon nanosheets may have various shapes due to the difference in dispersion force.

For example, the hybrid carbon nanosheets may have a flat shape without folding or bending, or may have a wrinkled shape. Specifically, the hybrid carbon nanosheets may have a flat shape in a solvent having a high polarity and may have a crumpled shape in a solvent having a low polarity.

In the quantum solvent, the unconjugated electrons of the oxygen-containing functional groups of the hybrid carbon nanosheets can be highly stabilized by hydrogen bonding with the quantum hydrogen atoms of the solvent. On the other hand, since the quantum hydrogen atoms forming the hydrogen bond are not present in the non-protonic solvent, the hybrid carbon nanosheets are wrinkled in shape to minimize the exposure of the electronegative oxygen atoms to the non-protic environment, and the oxygen content of the hybrid carbon nanosheets By maximizing the number of internal hydrogen bonds between the surface functional groups, the free energy of the hybrid carbon nanosheets is lowered and stabilized.

The hybrid carbon nanosheets may have an average particle diameter of 50 to 2000 nm. More specifically, the hybrid carbon nanosheet has an average particle diameter of 1000 to 2000 nm in a highly polar polar solvent such as water, ethylene glycol, or methanol, and has a low polarity. The hybrid carbon nanosheet has an average particle diameter of 50 to 500 nm in a solvent such as tetrahydrofuran (THF) It may have an average particle size of 500 nm.

As the structure of the hybrid carbon nanosheet varies depending on the degree of polarity of the solvent, the fluorescence characteristics of the hybrid carbon nanosheet are determined. In the quantum solvent, the structure of the nanosheet is maintained, so that the fluorescence in the graphene nanosheets and the carbon nanorings emit light at the same time. As a result, blue and orange fluorescence are emitted. However, in the non-magnetic solvent, the fluorescence emission of the carbon nanorings decreases due to the crumpled shape, and mainly the green fluorescence is emitted.

The tendency of such a solvent is determined by the following procedure based on the value of E _T (30), which is the solvent polarity parameter of the solvent, and the value of the Kamlet-Taft factor, which indicates the solvent acidity of the solvent Polar or non-polar solvent -> polar or quantum solvent): < RTI ID = 0.0 >

1: tetrahydrofuran (THF), 2: acetone, 3: N-methyl-2-pyrrolidone (NMP), 4: dimethylformamide (DMF), 5: dimethylsulfoxide (DMSO) Acrylonitrile (ACN) 7: isopropyl alcohol (IPA) 8: n-BuOH 9: ethanol (EtOH) 10: ethylene glycol monomethyl ether (EGME) 11: methanol MeOH), 12: ethylene glycol (EG), 13: water.

For example, in the present specification, a highly polar or quantitative solvent may refer to a solvent in which E _T (30) is in the range of 50 to 70 kcal / mol, or an alpha value in the range of 0.6 to 1.5. More specifically, in the present specification, a highly polar or quantitative solvent may refer to a solvent having an E _T (30) of 55 to 65 kcal / mol or an α value of 0.9 to 1.3. For example, the polar or highly polar solvent may be water, EG, MeOH, EGME, EtOH, n-BuOH, IPA, and the like.

In addition, in the present specification, a solvent having a low polarity or an aprotic solvent may refer to a solvent having an E _T (30) of 30 to 47 kcal / mol or a value of 0 to 0.4. More specifically, low polarity or non-polar solvents can be used herein to refer to solvents having an E _T (30) in the range of 35 to 45 kcal / mol or an alpha value in the range of 0 to 0.1. For example, the solvent having low polarity or non-polarity may be THF, acetone, NMP, DMF, DMSO, ACN and the like.

The solvent having a high polarity is typically water, and the solvent having a low polarity is typically dimethylformamide (DMF).

The hybrid carbon nanosheets vary in luminescence color depending on the polarity of the solvent, particularly the characteristics of the solvent such as hydrogen bonding (quantum or non-magnetic).

For example, when the hybrid carbon nanosheets are excited with light having a wavelength of about 360 nm, blue light (about 400 nm) is emitted in a solvent having a high polarity (for example, E _T (30) = 55-65 kcal / mol) (Peak at about 520 to 620 nm) in a solvent with a low polarity (eg, E _T (30) = 35 to 45 kcal / mol) It mainly emits light.

In addition, when the hybrid carbon nanosheets are excited with light having a wavelength of about 480 nm, orange-colored light (about 570 to 620 nm) is emitted in a solvent having a high polarity (e.g., E _T (30) = 55 to 65 kcal / mol) (peak at about 520 to 570 nm) in a solvent with a low polarity (eg, E _T (30) = 35 to 45 kcal / mol).

Particularly, in the hybrid carbon nanosheets, the shape changes according to the polarity of the solvent, thereby changing the luminescent color. For example, the hybrid carbon nanosheets have a flattened shape in a highly polar solvent (e.g., E _T (30) = 55-65 kcal / mol), while a solvent having a low polarity (for example, E _T 30) = 35 to 45 kcal / mol).

The shape of the hybrid carbon nanosheets and the change of the luminescent color can be reversibly and reproducibly generated depending on the solvent.

The hybrid carbon nanosheets vary in quantum yield depending on the polarity of the solvent. For example, the hybrid carbon nanosheets may have a quantum yield of 10 to 20% in DMF, while having a quantum yield of 20 to 30% in water when excited by light of a wavelength of about 360 nm. Further, when the hybrid carbon nanosheets are excited with light having a wavelength of about 480 nm, they may have a quantum yield of 15 to 25% in DMF, and a quantum yield of 5 to 15% in water.

In addition, the lifetime of the main emission band of the hybrid carbon nanosheet may vary depending on the polarity of the solvent.

As an example, the hybrid carbon nanosheets exhibit a blue band (peak at about 400-450 nm) when excited by light at a wavelength of about 375 nm, wherein the blue band has a lifetime of 4-6 ns in water, It can have a lifetime of 2 to 4 ns in DMF.

As another example, the hybrid carbon nanosheets exhibit yellow to orange bands (peaks at about 520 to 620 nm) when excited with light at a wavelength of about 375 nm, wherein the yellow to orange bands are between 1 and 3 ns in water While it can have a lifetime of 4-6 ns in DMF.

As another example, the hybrid carbon nanosheets exhibit yellow to orange bands (peaks at about 520 to 620 nm) when excited with light at a wavelength of about 450 nm, wherein the yellow to orange bands are present in the range of 0.1 to 2 ns , While it can have a lifetime of 4 to 6 ns in DMF.

The hybrid carbon nanosheets have excellent solvent discoloration characteristics that vary from blue to orange, and further to white depending on changes in solvent.

In particular, the hybrid carbon nanosheets of the present invention are understood to be the first materials that emit light to cover almost all the visible light region in accordance with changes in the solvent.

This full-color emission is caused by a change in the shape of the hybrid carbon nanosheets depending on the solvent, thereby causing solvent discoloring light emission.

Specifically, the degree of the surface functional group exposed to the solvent and the degree of hydrogen bonding between the solute and the solvent are changed by the change of the shape of the carbon nanosheets, and the non-radiative relaxation of the photoexcited surface functional group is changed, The spectrum of luminescence can be adjusted.

The hybrid carbon nanosheets can be used for applications such as optoelectronic devices, biological labels, and sensors. Thus, the present invention also provides optoelectronic devices, biological labels and sensors comprising the hybrid carbon nanosheets.

The present invention also provides a method for producing a nanocrystalline oxide film, comprising the steps of: (1) preparing a dispersion solution of graft oxide nanosheet; (2) adding a low molecular precursor including an organic acid and an amine compound to the dispersion solution to obtain a mixed dispersion solution; And (3) hydrothermally carbonizing the mixed dispersion solution. The present invention also provides a method for producing a hybrid carbon nanosheet.

Hereinafter, each step will be described in detail.

In the step (1), a dispersion solution of graft oxide nanosheets is prepared.

The graphene oxide nanosheets can be prepared by conventional methods. For example, the graphene oxide nanosheet can be obtained by peeling graphite powder by ultrasonic treatment.

The solvent used in the dispersion solution may be water, ethanol, DMF, or the like.

In the step (2), a low-molecular precursor including an organic acid and an amine compound is added to the dispersion solution obtained in the previous step to obtain a mixed dispersion solution.

The organic acid may comprise citric acid. Further, an organic acid other than citric acid, for example, chitosan, alginic acid, or a mixture thereof may be further added to the mixed dispersion solution.

The amine compound may be, for example, a C _2-10 alkylenediamine, more specifically, ethylene diamine.

The low molecular weight precursor may further include other compounds. As an example, the low molecular weight precursor may further include boric acid.

The equivalent ratio of the boric acid to the organic acid may be 1: 0.3-1.5, and may be 1: 0.5-1.3. When the equivalent ratio between boric acid and organic acid is within the above range, the quantum yield of the finally prepared carbon nanosheets can be further improved.

The equivalent ratio of the boric acid and the amine compound may be 1: 0.3-1.5, and may be 1: 0.5-1.3. When the equivalent ratio of the boric acid and the amine compound is within the above range, the optical characteristics and the like of the finally prepared carbon nanosheet can be more excellent.

In the step (3), the mixed dispersion solution obtained in the above step is hydrothermally carbonized to obtain a hybrid carbon nanosheet.

Through the hydrothermal carbonization process, carbon nanorings can be synthesized from the low-molecular precursor to be formed on the oxide graphene nanosheet.

Further, the graphene oxide nanosheets may be partially reduced during hydrothermal carbonization.

The hydrothermal carbonization may be carried out at a temperature in the range of 170 to 200 ° C, specifically in the range of 180 to 190 ° C, more specifically in the range of 180 to 185 ° C.

The present invention also relates to a hybrid carbon nanosheet; And at least one solvent.

Here, the hybrid carbon nanosheet may have the same structure as the hybrid carbon nanosheet described above, and may be manufactured by the same manufacturing method, so the content thereof will be omitted.

The solvent may also be selected from the group consisting of water, ethylene glycol, methanol, ethylene glycol monomethyl ether, ethanol, n-butanol, isopropanol, acrylonitrile, dimethylsulfoxide, dimethylformamide, Acetone, and tetrahydrofuran.

The hybrid carbon nanosheets in the solution may have various colors and shapes depending on the type of the solvent, and a detailed description thereof is as exemplified above.

The present invention also provides a method for producing a carbon nanostructure, comprising: (1) preparing a first solution by adding a hybrid carbon nanosheet to a first solvent; And (2) illuminating the first solution with excitation light to emit a first hue.

The method may further comprise, after step (2), (3) replacing the first solvent of the first solution with a second solvent to produce a second solution; And (4) irradiating the second solution with excitation light to emit a second color, wherein the first solvent and the second solvent have different polarities, and the first color and The second color may have different CIE color coordinates (x, y).

Here, the hybrid carbon nanosheet may have the same structure as the hybrid carbon nanosheet described above, and may be manufactured by the same manufacturing method, so the content thereof will be omitted.

The first solvent and the second solvent have different polarities. For example, the first solvent and the second solvent may be different from each other, and may be any one of aqueous solvent or organic solvent or a mixture of two or more thereof.

Specifically, the first solvent and the second solvent are different from each other and include water, ethylene glycol, methanol, ethylene glycol monomethyl ether, ethanol, n-butanol, isopropanol, acrylonitrile, dimethylsulfoxide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, acetone and tetrahydrofuran.

The first color emitted by irradiating the excitation light to the first solution and the second color emitted by irradiating the excitation light to the second solution have different CIE color coordinates (x, y). At this time, excitation light irradiated to the first solution and excitation light irradiated to the second solution may be light having the same wavelength.

That is, when the solvent is changed, the hybrid carbon nanosheets can emit different colors in the same irradiation light.

The hybrid carbon nanosheets may have different shapes in the second solvent than in the first solvent. For example, the hybrid carbon nanosheets may have a flattened shape when present in a quantum solvent, while they may have a wrinkled and agglomerated shape when present in an aprotic solvent. As the quantum solvent, water is typically exemplified, and the non-magnetic solvent is typically DMF.

The emission and shape changes of the hybrid carbon nanosheets can be reversibly and reproducibly performed depending on the solvent. That is, when the solvent is changed to the hybrid carbon nanosheets and then returned to the original solvent, the original shape can be recovered and the original color can be emitted again.

For example, the method of luminescing the hybrid carbon nanosheets may further comprise: after the step (4): (5) preparing a third solution by replacing the second solvent of the second solution with the first solvent; And (6) irradiating the third solution with excitation light to emit a third color, wherein the first color and the third color may have the same CIE color coordinate (x, y).

Hereinafter, the present invention will be described in more detail by way of examples. The following examples are illustrative of the present invention, but the present invention is not limited to the following examples.

The definitions of abbreviations used in the following examples are as follows.

- ACN, MeCN: acrylonitrile

- n-BuOH: n-butanol

- CD: carbon nanodot, carbon nanodot

- CIE: International Lighting Commission, Commission Inernationale De L'eclairage

- CNS: carbon nanosheet, carbon nanosheet

- CNS-DMF: CNS in DMF

- CNS-EtOH: CNS in EtOH

- CNS-water: CNS in water

- DLS: dynamic light scattering

- DMF: dimethylformamide

- DMSO: dimethylsulfoxide

- EDA: Ethylene diamine

- EG: ethylene glycol

- EGME: Ethylene glycol monomethyl ether

- EtOH: ethanol

- FT-IR: Fourier transform infrared spectroscopy

- GO: graphene oxide

- IPA: isopropyl alcohol

- MeOH: methanol

- NMP: N-methyl-2-pyrrolidone

- PL: photoluminescence

- QY: quantum yield, quantum yield

- THF: Tetrahydrofuran

- TCSPC: time-correlated single-photon counting, time-correlated single-photon counting

- XPS: X-ray photoelectron spectroscopy, X-ray photoelectron spectroscopy.

Materials used in the following examples were all purchased from Sigma-Aldrich unless otherwise noted.

Production Example 1: Preparation of oxidized graphene nanosheet

Graphite powder (Baycarbon) having a particle size of 45 μm was peeled by ultrasonic treatment according to the modified Hummer method to obtain a brown dispersion solution of oxidized graphene.

Example 1: Synthesis of Solvent Patchable Hybrid Carbon Nanosheet (CNS)

96 mg of citric acid (0.50 mmol, C ₆ H ₈ O ₇ ), 31 mg of boric acid (0.50 mmol, H ₃ BO ₃ ) were added to 10 mL of the GO dispersion solution (0.50 mg / mL) and an _{EDA (0.50 mmol, C 2 H} 8 N 2) was added 34.7 μL. After stirring for 10 minutes, the solidified black solution was placed in a Teflon-lined stainless steel autoclave. Hydrothermally carbonized at 180 DEG C for 6 hours to obtain a blackish brown solution (supernatant) and a black powder (precipitate). The precipitate was washed five times with ethanol and chloroform, and the solvent of the supernatant was evaporated in vacuo to give a powder.

Comparative Example 1

The same procedure as in Example 1 was repeated except that the low molecular weight was hydrolyzed without addition of the GO dispersion solution.

Experimental Example

In the following Experimental Examples, the absorption spectrum of CNS was obtained using a UV / Vis spectrophotometer (UV-2550, Shimadzu). The emission spectrum of CNS was measured using a fluorimeter (RF-6000, Shimadzu). The structure of the CNS was analyzed using XPS (K-alpha, Thermo Fisher) and FT-IR spectrometer (Cray 660, Varian). The shape and size of the CNS were observed using a transmission electron microscope (JEM-2100, JEOL). Fluorescence lifetime was measured using a TCSPC spectrometer (Fluotime 300, PicoQuant) and a picosecond-pulse diode laser (375 nm emission: LDH-D-C-375, PicoQuant, and 450 nm emission: LDH-D-C-450, PicoQuant). The total instrument response function (IRF) was 200-220 ps. The photoluminescence lifetime was calculated by substituting the photoluminescence decay curves of multiple exponential functions by software (FluoFit, PicoQuant).

Figure 1 shows the synthesis and optical properties of the CNS, wherein (a) is a schematic representation of the method of synthesis of the hybrid CNS, (b) shows the CNS dispersion solution in different solvents (concentration 0.10 mg / This is an optical image when excited. For comparison, the carbon nano ring powder of Comparative Example 1 in which solvent discoloration was not observed was tested in representative solvents. The figure shows the order of low polarity to high polarity in the order of E _T (30) of the solvent.

As shown in Fig. 1 (a), CNS can be prepared by hydrolyzing a small molecule such as citric acid, boric acid and ethylene diamine in the presence of a GO nanosheet. Using GO nanosheets as a graphite frame, decomposition by hydrothermal reaction occurred on the surface of the GO nanosheet.

Other carbonaceous residues were all removed during washing and precipitation with a mixture of chloroform and ethanol.

On the other hand, the final product separated from the supernatant after the purification step was identified as a graphene-like sheet having clusters of nanorings.

CNS powders were recovered and then re-dissolved by varying the polarity of the solvent. As a result, excellent solvent discoloration was confirmed from the CNS dispersion solution as shown in FIG. 1 (b), FIG. 5 and FIG.

Figure 2 shows the (A) to (c) show UV / Vis and photoluminescence spectra of CNS in water, EtOH and DMF, respectively. Here, the photoluminescence spectrum of CNS was obtained under irradiation of a wavelength of 40 mn from 360 nm to 480 nm. (Water), 575 nm (EtOH), and 550 nm (EtOH) at 430 nm, FIG. 2 (d) (Normalized PL decay profiles) of the CNS in the three representative solvents observed in DMF. The excitation wavelengths at this time are shown in the respective figures.

Water, ethanol (EtOH), and dimethylformamide (DMF) were chosen as representative solvents with different polarities to further explore the photophysical properties of CNS in various solvents. In the present invention, CNS dispersion solutions using these solvents are referred to as CNS-water, CNS-EtOH, and CNS-DMF, respectively.

The UV / Vis spectrum of each dispersion solution showed an absorption band at about 330 nm and about 500 nm.

Of these, the 330 nm band is due to the n-π * transition of the carbon nanomaterial with oxygen defects and the band near 500 nm is the characteristic peak of the CNS.

It is known that various surface states are formed depending on the oxidation state of the surface functional groups, and as a result the extinction curve can extend beyond 400 nm.

These bands can thus be placed in the visible range by electrical transfer of the surface state of the CNS.

It was found that the photoluminescence of CNS varies greatly depending on the solvent and is very sensitive to the excitation wavelength. In particular, two emission bands of 430 nm or less and 550 to 590 nm were observed in all the solvents under the 360 nm excitation wavelength (see FIGS. 5 and 6).

Blue light emission was mainly observed in water, while in the lower polarity EtOH and DMF, the yellow to orange band (550-590 nm) was gradually increased.

When excited at 480 nm, the main emission band of yellow (550 nm) was shown in DMF, but it changed to orange (590 nm) in water to clearly show solvent discoloration.

The yellow to orange bands are due to the surface state, which is because the selectively excited surface state is formed and the position of the band (550-590 nm) varies greatly depending on the solvent.

Table 1 below shows the quantum yield (%) of CNS in water, ethanol and DMF.

Excitation wavelength CNS-water CNS-EtOH CNS-DMF 360 nm ^a 23.1% 18.0% 14.3% 480 nm ^b 8.9% 16.7% 20.2% ^a Reference substance: quinine sulfate (QY = 54% in 0.10 MH ₂ SO ₄ )
^b Reference substance: Rhodamine 6G (QY = 95% in ethanol)

As shown in Table 1 above, under 480 nm visible light excitation, the quantum yield (QY) of CNS in DMF was measured as 20.2%, which was about twice the quantum yield of CNS in water (8.9%).

In addition, solvent-dependent optical properties were examined by preparing a mixed solvent in which water and DMF were mixed at different ratios, and then dissolving the CNS.

As a result, as shown in FIG. 7, as the ratio of water to DMF decreased, the emission of CNS changed and the photoluminescence intensity increased. Specifically, a blue main band having a maximum peak at 430 nm in water was shown at a 360 nm excitation wavelength, but it was separated into a double band at 430 nm and 538 nm in a water / DMF (1: 1) mixed solvent , And a single band with a peak at 548 nm in pure DMF. It can be seen that the CNS is greatly affected by the solvent polarity.

It was found that the relative intensities of the two photoluminescent main bands are due to the change in lifetime of the two bands depending on the solvent (see FIGS. 2 (d) to (f)).

Table 2 below shows the excited state lifetime of the CNS in water, ethanol and DMF. At this time, the emission wavelength was selected depending on the type of the solvent.

Average Life (ns) λ _ex = 375 nm λ _ex = 450 nm ? _em (nm) 430 550 575 590 550 575 590 CNS-water 5.2 - - 1.9 - - 0.8 CNS-EtOH 3.4 - 3.1 - - 2.8 - CNS-DMF 3.0 5.0 - - 4.9 - -

As shown in Table 2 and FIG. 2 (d), the disappearance of the blue band was accelerated by changing the solvent from water to EtOH or DMF, and the weight-average lifetime decreased from 5.2 ns to 3.0 ns.

The relaxation time of the yellow to orange bands was increased from 1.9 ns to 5.0 ns at an excitation wavelength of 375 nm as the solvent was changed from water to EtOH or DMF (see Fig. 2 (e)), To 4.9 ns at 0.8 ns (see Fig. 2 (f)).

Therefore, it can be seen that the shape of the photoluminescence spectrum is determined by the lifetime of the two bands depending on the change of the solvent.

3, Lt; RTI ID = 0.0 > CNS < / RTI > Figures 3 (a) and 3 (b) are TEM images of the CNS in water, and Figures 4 (c) and 4 (d) are TEM images of the CNS in DMF and each sample was observed after removal of the solvent. 3 (a) and 3 (c) are the particle size distribution histograms measured by DLS for CNS in water and DMF, respectively. FIG. 3 (e) shows the hydrodynamic diameter (D _h ) of the CNS according to the solvent as a volume average fraction measured by DLS, wherein the open label represents the main component and the closed label represents the minute components (n = 10).

3 (a) and 3 (b) , CNS-water was observed with a transmission electron microscope (TEM). As a result, a nanorring having a diameter of 15 nm was confirmed together with a structure similar to a graphene sheet. The interlayer distance in the crystalline carbon nanorings was found to be 0.34 nm, which corresponds to the (002) plane spacing of graphene in a high resolution TEM image. These carbon nanorings appear to be formed by carbonization of the molecular precursor on the graphene sheet in the hydrothermal reaction.

In contrast, as shown in FIGS. 3 (c) and (d), CNS-DMF was observed to have a folded and wrinkled shape with an average diameter of 110 ± 10 nm. The DMF dispersion solution could have a very stable state without special aggregation for several months.

In addition, it was confirmed by DLS analysis that the hydrodynamic mean diameters were 1280 ± 330 nm and 310 ± 20 nm, respectively, in water and DMF. The size of the CNS was measured reproducibly, even when some deviation in size measured by TEM in the dry state was taken into account.

In addition, the shape of the CNS was dependent on the polarity of the solvent, particularly the properties of the solvent (quantum vs. non-magnetism) such as hydrogen bonding (see Figure 3 (e)). In particular, as shown in Fig. 8, the sheet shape was observed in the quantum solvent, and the folding structure of the CNS was observed in the non-magnetic solvent.

In particular, as shown in Fig. 9, when the solvent was changed from DMF to water or vice versa, reversible shape change and spectroscopic characteristics were observed. These results indicate that the shape of the CNS varies greatly depending on environmental conditions.

In order to further investigate that the optical characteristics are controlled by changing the shape of the CNS according to the solvent, the powder of Comparative Example 1 which has undergone the hydrothermal reaction of the low molecular weight precursor without the graphene oxide nanosheets was tested and shown in FIG. As shown in FIG. 10, the carbon nanoparticles prepared in Comparative Example 1 exhibited a carbon nanorring-like structure having an average particle diameter of 20 nm, and emitted blue light of a wavelength of about 440 nm regardless of the polarity of the solvent. Unlike the CNS or oxidized graphene nanosheets of Example 1, the carbon nanorings of Comparative Example 1 were not well dispersed in relatively low polarity solvents such as EtOH or DMF. Considering these results, it appears that graphite carbon nano-rings with low solubility are fixed on the surface of the graphene nanocrystalline oxide sheet and cause the shape change.

The solubility depends on the physical interaction between the solute and the solvent molecule.

In order to explain the interaction of the molecules, the chemical composition of the CNS needs to be confirmed, and FT-IR and XPS were performed for this.

11, the CNS is characterized by 1375 cm ^-1 (CH ₂ bending), 1465 cm ^-1 (CH ₃ bending), and 1591 cm ^-1 (C = C stretching) and at 2846, 2923 and 2956 cm ^-1 Gt; IR < / RTI > It also showed broad peaks at about 3249 cm ^-1 (OH and NH stretching). According to the XPS results, the intensity of oxygen-containing functional groups decreased while the solvent was changed from water to DMF, while sp ³ conjugation increased.

Figures 12 (a) - (c) are deconvoluted high resolution C1s XPS spectra of CNS-water, CNS-EtOH and CNS-DMF, respectively. Because of folding and wrinkling in low polarity solvents, the oxygen groups of the CNS are significantly reduced and the proportions of sp ² - and sp ³ - carbon in ethanol and DMF are different from those in water.

Table 3 below also shows the chemical composition of CNS-water and CNS-DMF by XPS.

CNS-water CNS-DMF Carbon C 1s Dislocation (eV) % Dislocation (eV) % C = C 284.25 31.44 284.28 19.56 C-C 285.12 27.54 285.02 69.03 C-N 286.14 19.28 286.28 6.39 C-O 287.16 10.23 287.12 2.64 C = O 288.07 8.85 288.16 1.82 COOH 289.34 2.64 289.22 0.53

As shown in Table 3 and FIG. 12, the content of oxygen groups such as hydroxyl group, carbonyl group and carboxylic acid group in the deconvoluted high-resolution C1s XPS spectrum is represented by a high content (about 22%) in CNS-water, -DMF to about 5%. Also, when the solvent was changed from water to DMF, the ratio of sp ² - to sp ³ - region in C1s changed from 1.14 to 0.28.

Considering that the probe depth of XPS is up to several nanometers and that the chemical composition identified from XPS is reversibly reproducible in response to solvent changes, the decrease in the content of oxygen-containing functional groups in DMF in the XPS measurement is due to the fact that in the DMF, It can be inferred that the exposure of the surface functional groups is folded in a direction that minimizes exposure. The results from the XPS measurements fit well with the TEM and DLS results.

Figure 4 shows the solvent discoloration characteristics of the CNS, wherein (a) shows that the photoluminescent band excited at 480 nm is shifted from yellow to yellow according to changes in solvent polarity (E _T (30)) and acidity (Kamlet-Taft acidity, Indicates a Stokes shift in orange. FIG. 4 (b) is a schematic diagram showing the changed shape of the CNS in the polar and non-polar solvents, and FIG. 4 (c) shows the energy diagram of the CNS according to the solvent. 4 (d), the CIE chromaticity coordinates (x, y) on the left and right sides are calculated from the photoluminescence spectra obtained from solvents having different polarities at 360 nm and 480 nm, respectively, Lt; RTI ID = 0.0 > 360 nm < / RTI > and 480 nm, respectively. In the CIE color coordinates (x, y), each solvent is indicated by the following number. 1: THF, 2: acetone, 3: NMP, 4: DMF, 5: DMSO, 6: ACN, 7: IPA, 8: n- BuOH, 9: EtOH, 10: EGME, 13: Water.

Figure 13 also shows the stokes shift associated with the solvent polarity parameters Kamlet-Taft parameters ([beta] and [pi] *), indicating that [beta] and [pi] * are not associated with the Stokes shift of the CNS .

Based on the chemical structure of the CNS, the properties of solute-solvent interactions (i.e., solvation) can be described at the molecular level.

Solvation involves non-specific interactions and specific interactions, which are each due to the bipolarity / polarization ratio and the degree of hydrogen bonding of the solvent.

The E _T (30) index of the solvent generally indicates the polarity of the solvent, which is obtained from the phenomenological solvent discoloration of the dye in various solvents. In addition, Kamlet-Taft (KT) parameters α, β, and π * can be used to categorize the specific / non-specific solvation characteristics of the solvent. The? And? Values of the solvent mean the characteristics of the solvent capable of giving or receiving a hydrogen bond, respectively, and? * Means the degree to which the solvent can stabilize the charge / dipole property by the dielectric effect.

Among these parameters, as shown in Fig. 4 (a), the curve for the K-T acidity parameter of the solvent shows a clear correlation.

As can be seen from the solvent-dependent photoluminescence lifetime of green to orange bands ranging from 4.9 ns (CNS-DMF) to 2.8 ns (CNS-EtOH) to 760 ps (CNS-water) The excited state life of organic dyes having bondable oxygen-containing groups generally tends to decrease.

In general, the hydrogen bonding between the unbound electrons of the oxygen-containing surface functional group and the quantum hydrogen of the solvent molecule is very important for solvation of the CNS.

Considering the solvent discoloration and shape variability test results of the CNS according to the solvent, the following shape-induced solvent discoloration mechanism can be suggested.

First, CNS reversibly folds and unfolds the geometrical variation. This is mainly due to the specific solvation of CNS by hydrogen bonding with quantum solvent molecules (see FIG. 4 (b)).

In protonic solvents, the unconjugated electrons of the oxygen-containing functional groups of the CNS can be highly stabilized by hydrogen bonding with the quantum hydrogen atoms of the solvent. However, such coupling is reduced in aprotic solvents, and the CNS then finds a path to the lowest free energy. To this end, the CNS maximizes the number of internal hydrogen bonds between the oxygen-containing surface functional groups of the CNS while minimizing the exposure of electronegative oxygen atoms to a non-protic environment by wrinkling the shape.

Second, the change in photoluminescence according to the shape of the CNS is due to the difference in the lifetime of the two main photoluminescent bands (see Fig. 4 (c)).

When the CNS is flat without bending, the oxygen containing functional groups become hydrogen bonded to the quantum solvent molecules. This accelerates the non-radiative transition of the surface state, so that the green to orange bands appearing in the oxidized graphene nanosheets have a shorter excitation life than the blue bands in the carbon nanorings. When the CNS is in the form of a crumpled and agglomerated layer, the lifespan of the green to orange bands increases because there is no effective oscillatory relaxation on the solvent molecules.

On the other hand, the resonance energy is transferred to the adjacent surface region of the oxide graphene nanosheet by the CNS folding, so that the relaxation channel for the blue emission of the carbon nanorings is opened, so that the blue region emission can be absorbed in the aggregated shape. In addition, the weight-average lifetime of the blue light-emitting band is reduced in the aprotic solvent than in the quantum solvent, specifically 5.2 ns in CNS-water but 3.0 ns in CNS-DMF.

The transfer efficiency (E) of the resonance energy is closely related to the distance between donor and acceptor, which controls the lifetime of the donor according to the equation E = 1 - τ _F / τ _D , where τ _D is the photoluminescence And τ _F is the lifetime shortened by the resonant energy carrier. Where τ _F is obtained as the average weight of multiple exponential decay of CNS photoluminescence and τ _D is derived from the photoluminescence lifetime of the carbon nanorning sheet dispersed in water. As a result, the efficiency of the resonance energy transfer was calculated as 0.1, 0.4 and 0.5 in water, EtOH and DMF, respectively.

As a result, the lifetime of the two main photoluminescent bands and the degree of excitation depend on the dispersion solvent and the excitation wavelength of the CNS, and accordingly, the relative intensities of the two photoluminescent bands are changed, It is interpreted as changing.

Thus, it was observed that the CIE color coordinates (x, y) were changed due to the strong influence of the light emission of the CNS on the solvent. Emission colors having CIE color coordinates in various regions were observed according to the change of the solvent in the 360 nm excitation light (see Fig. 4 (d)). In particular, among the various solvents, the CIE chromaticity coordinates (0.30, 0.33) of the CNS dispersed in IPA are similar to the white CIE color coordinates (0.33, 0.33), which is very useful in the field of optoelectronics.

As shown in Experimental Examples 1 to 4, the solvent-discoloring carbon nanosheets could be prepared by hydrothermally carbonizing the low-molecular precursor using the GO nanosheet as a frame. Due to clusters of large amounts of surface oxygen groups and carbon nanorings in the hybrid carbon nanosheets, excitation-dependent behavior in CNS-water was observed. Structural / photophysical analysis, such as XPS, FT-IR spectroscopy and TCSPC, confirmed that the CNS showed green luminescence due to internal hydrogen bonds that were crumbled when the solvent was changed to non-polar DMF. The characteristics of such hybrid carbon nanostructures are synergistic with each other and exhibit unpredictable effects, thereby providing an opportunity to further utilize the optical characteristics of the carbon nanomaterial. Accordingly, the solvent-discolorable hybrid CNS according to the present invention can be usefully used in optoelectronic devices and sensors.

Claims (20)

Oxidized graphene nanosheet; And
And carbon nanoring formed on the graphene oxide nanosheet,
Wherein the shape and luminous color of the hybrid carbon nanosheet vary depending on the polarity of the solvent when present in the solvent.
delete The method according to claim 1,
Wherein the shape of the hybrid carbon nanosheets and the change in luminescent color occur reversibly and reproducibly depending on the solvent.
The method according to claim 1,
Is crimped in a solvent with the hybrid carbon nano-sheet, 55 ~ 65 kcal / mol of E _T (30) flat and has an expanded shape, 35 ~ 45 kcal / mol of E _T (30) in a solvent having a united shape Wherein the hybrid carbon nanosheets have a thickness of at least 100 nm.
5. The method of claim 4,
The hybrid carbon nanosheets emit blue light in a solvent having an E _T (30) of 55 to 65 kcal / mol when excited with light having a wavelength of 360 nm, and emit blue light of 35 to 45 kcal / mol _And emits light of a yellow to orange series in the solvent having _T (30).
6. The method of claim 5,
The hybrid carbon nanosheets emit orange light in a solvent having an E _T (30) of 55 to 65 kcal / mol when excited with light having a wavelength of 480 nm, and emit light of E in a solvent having a _T (30) it is for emitting light in the yellow-based, hybrid carbon nanosheets.
The method according to claim 1,
The hybrid carbon nanosheet
A hybrid carbon nanosheet obtained by hydrothermal carbonization of a low molecular weight precursor in the presence of an oxidized graphene nanosheet.
The method according to claim 1,
Wherein the carbon nanorings are doped with nitrogen (N) and boron (B).
9. The method of claim 8,
Wherein the carbon nanorings have a diameter of 10 to 20 nm and the graphene oxide nanosheets have an average particle diameter of 50 to 2000 nm.
The method according to claim 1,
Wherein the carbon nanorings are formed at a ratio of 180 to 230 pieces / 占 퐉 ² per unit area (占 퐉 ² ) of the graphene oxide grains.
An optoelectronic device comprising the hybrid carbon nanosheet of claim 1.
Preparing a dispersion solution of the oxidized graphene nanosheet;
Adding a low molecular precursor including an organic acid and an amine compound to the dispersion solution to obtain a mixed dispersion solution; And
The method for producing hybrid carbon nanosheets according to claim 1, comprising the step of subjecting the mixed dispersion solution to hydrothermal carbonization.
13. The method of claim 12,
Wherein the organic acid comprises citric acid.
13. The method of claim 12,
Wherein the low molecular weight precursor further comprises boric acid.
13. The method of claim 12,
Wherein the hydrothermal carbonization is performed at a temperature of 180 to 185 ° C.
The hybrid carbon nanosheet of claim 1; And
But are not limited to, water, ethylene glycol, methanol, ethylene glycol monomethyl ether, ethanol, n-butanol, isopropanol, acrylonitrile, dimethylsulfoxide, dimethylformamide, N- And at least one solvent selected from the group consisting of hydrogen chloride, hydrogen chloride, and furan.
(1) adding the hybrid carbon nanosheet of claim 1 to a first solvent to prepare a first solution; And
(2) irradiating the first solution with excitation light to emit a first hue.
18. The method of claim 17,
After step (2) above,
(3) preparing a second solution by replacing the first solvent of the first solution with a second solvent; And
(4) irradiating the second solution with excitation light to emit a second color,
Wherein the first solvent and the second solvent have different polarities,
Wherein the first color and the second color have different CIE color coordinates (x, y).
19. The method of claim 18,
The hybrid carbon nanosheet
Wherein the second solvent has a different shape in the second solvent than in the first solvent.
19. The method of claim 18,
The method for luminescence of the hybrid carbon nanosheets is characterized in that after the step (4)
(5) replacing the second solvent of the second solution with the first solvent to produce a third solution; And
(6) irradiating the third solution with excitation light to emit a third color,
Wherein the first color and the third color have the same CIE color coordinate (x, y).

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