KR101556584B1 - N-type graphene quantum dots and method for manufacturing the same by nitrogen doping - Google Patents

Abstract

The present invention relates to a method for preparing a bare graphene quantum dot comprising: treating a bare graphene quantum dot with a nitrogen containing compound; And heat treating the resultant. The present invention also relates to a method for producing an n-type graphene quantum dot and a graphene quantum dot doped with nitrogen (N) atoms.

Description

TECHNICAL FIELD [0001] The present invention relates to an n-type graphene quantum dot and an n-type graphene quantum dot by nitrogen doping,

The present invention relates to an n-type graphene quantum dot and a method for producing n-type graphene quantum dot by nitrogen doping.

Graphene quantum dots (GQDs) are conductive two-dimensional nanoparticles of sp ² hybridization with an atomic thickness of carbon and exhibit very unique optical and electrical properties depending on their size, shape, and edge state.

At these atomic layer thickness graphene quantum dots, the pi (π) electron states have high conductivity because they supply free charge carriers. However, their electronic structure strongly depends on the edge and size of the graphene quantum dot. Thus, the physical and electrical properties of graphene quantum dots can be controlled by changing their size and edge state. In particular, carbon nanomaterials can effectively control intrinsic properties such as electron state, surface and local chemical properties by doping heteroatoms.

One embodiment of the present invention is to provide n-type graphene quantum dots doped with nitrogen (N) atoms.

Another embodiment of the present invention is to provide a method for manufacturing an n-type graphene quantum dot at a low cost by simplifying the doping process of nitrogen atoms.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing the same.

According to an embodiment of the present invention, an n-type graphene quantum dot includes a single bond of carbon and nitrogen, a double bond of carbon and nitrogen, or a bond of carbon and nitrogen to the edge of a bare graphene quantum dot. A single bond of nitrogen and a double bond of carbon and nitrogen may be present.

An n-type graphene quantum dot according to an embodiment of the present invention is a single quantum well structure in which a single bond of carbon and nitrogen, a double bond of carbon and nitrogen, a single bond of carbon and nitrogen, and a double bond of carbon and nitrogen Can be an n-type graphene quantum dot having a relatively increased size compared to the size of a bare graphene quantum dot.

According to another aspect of the present invention, there is provided a method of manufacturing an n-type graphene quantum dot comprising: treating a bare graphene quantum dot with a nitrogen-containing compound; And heat treating the resultant.

According to another embodiment of the present invention, there is provided a method of manufacturing an n-type graphene quantum dot, comprising: preparing a bevel graphene quantum dot aqueous solution by mixing a bare graphene quantum dot with deionized water; Preparing hydrazine mixed solution by adding hydrazine to the aqueous solution of bare graphene quantum dots; And reacting the hydrazine mixed solution at a temperature of 30 to 180 ° C for 10 to 24 hours.

Specific details of other embodiments will be described in detail with reference to the detailed description and experimental examples.

In one embodiment of the present invention, a nitrogen impurity level (N impurity level) between a high occupied molecular orbital (HOMO) and a lowest occupied molecular orbital (LUMO) in the energy band structure of a bare graphene quantum dot It is possible to provide n-type graphene quantum dots in which absorption and luminescence characteristics are changed.

According to another embodiment of the present invention, there is provided a method for manufacturing n-type graphene quantum dots, comprising the steps of: (a) providing a bare graphene quantum dot with a nitrogen-containing compound; It is possible to provide an n-type graphene quantum dot having excellent price competitiveness.

Further, the n-type graphene quantum dot manufacturing method according to another embodiment of the present invention is composed of a simple step of one-step or two-step process of treating a nitrogen-containing compound to a bare graphene quantum dot and performing heat treatment, It is possible to solve the problem that the nitrogen atom is lost in the process and the yield is lowered. Therefore, there is an advantage that n-type graphene quantum dots can be provided at a high yield.

1 is an electron microscope image of graphene quantum dots before the hydrazine treatment.
2 is an electron microscope image of the graphene quantum dot after the hydrazine treatment.
3 is a high-resolution electron microscope image of a graphene quantum dot that is typically observed.
4 is a line profile corresponding to the white line in Fig.
5 is a magnitude distribution graph of quantum dots (GQDs) before nitrogen atom doping.
6 is a magnitude distribution graph of quantum dots (Hy-GQDs) after nitrogen atom doping.
7 is a C 1s XPS spectrum of a quantum dot (GQD) before nitrogen atom doping and a quantum dot (Hy-GQD) doped with nitrogen atoms.
FIG. 8 is a graph summarizing the relative intensities of the XPS peaks of the quantum dot (GQD) before the nitrogen atom doping and the nitrogen atom-doped quantum dot (Hy-GQD) in FIG.
9 is a N1s XPS spectrum of a quantum dot (GQD) before the hydrazine treatment and a quantum dot (Hy-GQD) after the hydrazine treatment.
10 is a graph summarizing the relative intensities of the XPS peaks of the quantum dot (GQD) and the processed quantum dot (Hy-GQD) before the hydrazine treatment in FIG.
11 is an electron loss spectrum (EELS) of C K-edge and N K-edge.
12 is a Raman spectrum before and after doping with nitrogen atoms.
13 is an energy band of a graphene quantum dot doped with nitrogen atoms.
14 is a light absorption spectrum of graphene quantum dots doped with nitrogen atoms.
15 is a photoluminescence graph of graphene quantum dots doped with nitrogen atoms.
16 is a graph of the optical luminescence lifetime of graphene quantum dots doped with nitrogen atoms.

Advantages and features of a manufacturing method according to an embodiment of the present invention and a method of achieving them will be made clear with reference to the embodiments and experiment examples described in detail below with reference to the accompanying drawings.

The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

< Example  : N atom doping Grapina Quantum dot  Production>

Bear Grapina Quantum dot  making

Bearing graphene quantum dots can be manufactured by various methods known in the art to which the present invention belongs. The bare graphene quantum dot according to an exemplary embodiment of the present invention can be manufactured using, for example, Hummers methods.

Specifically, exemplary bare graphene quantum dots of the present invention are prepared by preparing a graphene oxide sheet from graphite and chemically processing the graphene oxide by repeated oxidation and reduction and heat treatment of the various compounds After making the dispersion, graphene quantum dots (GQDs) of various sizes can be prepared by coating the dispersion on a substrate. In addition, a graphene quantum dot having a uniform size and shape can be fabricated by filtering using a nanopore membrane (see ACS Nano 6, 8203 (2012) for further details).

The inventors of the present application fabricated a 5-nm-sized bare graphene quantum dot using a humming method.

N atom doping Grapina Quantum dot  making

Exemplary N atom doping graphene quantum dots of the present invention can be fabricated by treating the bare graphene quantum dot with a nitrogen containing compound and heat treating the resultant.

Nitrogen (N) atoms are similar in size to carbon atoms and have five outermost electrons, so they can easily bond to carbon atoms. Since the bare graphene quantum dots contain 5 to 10% of Oxygen functional groups (OFGs), the oxygen bond groups of the graphene quanta are exposed to the nitrogen containing compound, as in the graphene oxide produced by the chemical method Can be removed more easily. At the same time, N atoms remain in the quantum dots. The oxygen bonding group may be C-O, C = O, O-C = O.

The nitrogen-containing compounds, poly pie roll _{((C 4 H 2 NH)} n), polyaniline (polyaniline), melamine _{(C 3 H 6 N 6)} , PDI (N, N'-bis (2,6-diisopropyphenyl) At least one compound selected from the group consisting of polyacrylonitrile (PAN), urea (CO (NH ₂ ) ₂ ), ammonia (NH ₃ ) and hydrazine (N ₂ H ₄ ) Lt; / RTI &gt;

In particular, since hydrazine contains a large amount of N atoms, carbon can be easily bound to N atoms by exposing the graphene quantum dots to hydrazine.

Illustratively, a hydrazine mixed solution is prepared by mixing a bare graphene quantum dot with deionized water to prepare an aqueous solution of a bare graphene quantum dot solution, adding hydrazine to the aqueous solution of the bare graphene quantum dots, and then mixing the hydrazine mixed solution at 30 to 180 ° C N-atom doped graphene quantum dots can be prepared by reacting at a temperature of 10 to 24 hours. By adjusting the hydrazine concentration, the reaction temperature and the reaction time, the doping concentration of the N atom in the final graphene quantum dot can be controlled. The hydrazine may be hydrazine monohydrate.

The inventors of the present application found that a 5-nm-sized bare graphene quantum dot was mixed with 10 ml of pure water and added with 0.5 ml of hydrazine monohydrate (65% N ₂ H ₄ ) For 10 hours to prepare graphene quantum dots doped with N atoms.

However, the size of the bare graphene quantum dot is not limited to 5 nm, and the nitrogen atom doping method of the present invention can be applied to all graphene quantum dots of various sizes.

< Experimental Example >

We successfully and structurally and optically verified the successful doping of N atoms in the 5 nm sized bare graphene quantum dots fabricated according to the fabrication method described above.

Hydrazine  Before and after treatment Grapina Quantum dot  Electron microscope image

1 and 2 are electron microscope images of the quantum dots before and after the hydrazine treatment. Fig. 3 is a high-resolution electron microscope image of a quantum dot typically observed, and Fig. 4 is a line profile corresponding to the white line in Fig.

As in the results of electron microscopy and line profiles, graphene quantum dots exhibit high single crystal properties before and after hydrazine treatment.

In graphene quantum dots, N bonds with carbons in the form of Graphitic N, pyridinic N, and pyrrolic N. On the plane, Graphitic N is understood as an N atom existing in the central region of the graphene quantum dot, and pyridinic N is understood as an N atom existing in the edge region of the graphene quantum dot, and pyrrolic N is located between the central region and the edge region As the N atom present in the nucleus.

The doped N atoms are expected to be located on the planar surface of the graphene quantum dot or in the edge region rather than the inner central region, and the physical and electrical properties of the graphene quantum dot can be controlled by doping N atoms.

5 is a magnitude distribution graph of quantum dots (GQDs) before nitrogen atom doping. 6 is a magnitude distribution graph of quantum dots (Hy-GQDs) after doping.

As shown in the electron microscopic results, graphene quantum dots have various size distributions, and the size distributions of the quantum dots before and after the nitrogen atom doping (denoted as GQDs and Hy-GQDs, respectively) in FIGS. 5 and 6 were analyzed.

Histogram analysis showed that the average size of the quantum dots prior to nitrogen atom doping was 5.03 ± 0.05 nm and 5.55 ± 0.05 nm after doping.

This means that the doped N after the hydrazine treatment was located at the edge of the graphene quantum dot.

X- ray Photoelectron Spectroscopy

FIG. 7 is a C 1s XPS spectrum of a quantum dot (GQD) before doping with nitrogen atoms and a doped quantum dot (Hy-GQD). 8 is a graph summarizing the relative intensities of respective XPS peaks.

C 1s XPS spectra can be separated into four XPS peaks at positions of 284.9, 285.6, 286.5, and 288.9 eV by Gaussian fitting method, which are respectively CC / C = C, CO, C = Lt; RTI ID = 0.0 &gt; = O &lt; / RTI &gt;

In this case, CC / C = C (sp ² C) is the XPS peak of the bond between carbons and CO, C═O and OC═O are XPS peaks related to oxygen-functional groups (OFGs) .

After hydrazine treatment, the XPS intensity of the oxygen functional groups decreases and the sp ² C occupancy increases from about 38% to 70%. Which means that oxygen functional groups have been reduced by hydrazine treatment in graphene quantum dots.

N 1s XPS  spectrum

9 is a N1s XPS spectrum of a quantum dot (GQD) before the hydrazine treatment and a quantum dot (Hy-GQD) after the hydrazine treatment. 10 is a graph summarizing the relative intensities of the XPS peaks of the quantum dot (GQD) and the processed quantum dot (Hy-GQD) before the hydrazine treatment in FIG.

The XPS spectra of N 1s were analyzed in detail to analyze the state of N atoms contained in the graphene quantum dots before and after the hydrazine treatment.

As shown in FIG. 9, three XPS peaks were observed in the graphene quantum dots such as 401.6 eV (pyridinic N), 400.5 eV (pyrrolic N), and 398.4 eV (graphite N), which were named N1, N2 and N3, respectively.

Relative XPS intensities of N1, N2 and N3 before and after the hydrazine treatment of graphene quantum dots are shown in FIG.

Before doping, the pyrrolic N component predominates, and after doping the pyridinic N component predominates. Graphitic N graphene substitutes one position of carbon in hexagonal ring of graphene, and its share does not change before and after hydrazine.

As a result of the XPS, the hydrazine-doped N atom is located at the edge of the graphene quantum dot and most of it is pyridinic N.

Electronic Energy Loss Spectrum ( EELS )

11 is an electron loss spectrum (EELS) of C K-edge and N K-edge.

EELS intensity related to C is most strongly observed in the EELS spectrum before and after nitrogen atom doping, which means that C is the most among the elements constituting the graphene quantum dot.

Two EELS peaks (279.4 eV, 290.8 eV) are observed in the C K-edge region. The peak at 279.4 eV is due to electrons (1s → π *) that transition to the π * level at the 1s level of C, while the peak at 290.8 eV is the electron (1s → σ *) that transitions from 1s to C * .

The NEL-related EELS peak (NK-edge region) is observed only after doping. Two EELS peaks appear similar to the C K-edge region, with 400.6 eV and 409.6 eV peaks appearing due to 1s → π * and 1s → σ * of C-N / C = N, respectively. The reason why the N-related EELS peak was not observed before the doping although the N may be included in the quantum dot manufacturing process even before the doping is considered is that the amount of N contained in one quantum dot is very small considering the resolution of EELS It is determined that N can not be detected.

Since the EELS peak associated with N is clearly observed after doping, a relatively large amount of N is doped into the quantum dots by the hydrazine treatment.

Raman Spectrum

12 is a Raman spectrum before and after doping.

Bear yes ~ 1360 cm from the pin ^QD-Raman peak of ¹ and ~ 1594 cm ^-1 is called D and G becomes the peak, each of which is corresponding gender defect (or edge) and crystal. The ratio of Raman intensity of D and G peak (I _D / I _G ) represents the degree of defect in the graphene quantum dot.

I _D / I _G before nitrogen atom doping is 0.98 and decreases by 0.93 to 0.93 after hydrazine treatment. This means that the ratio of total defects has decreased because N enters the vacancies of carbon at the edge of the bear graphene quantum dot to form a complete hexagonal structure.

In Raman spectra, the peak of D peak did not change much before doping, while the peak of G peak shifted from 1594 to ~ 1586 cm ^{- 1} . Generally, the change in G peak in graphene reflects the type of doping, indicating that the red transition is the n-type and the blue transition is the p-type graphene.

That is, it can be seen that the n-type graphene quantum dots are formed by the nitrogen impurities generated by the hydrazine treatment.

N valence Doped Grapina Quantum dot  Energy band and light absorption spectrum

13 is an energy band of a graphene quantum dot doped with N atoms. 14 is a light absorption spectrum of a graphene quantum dot doped with N atoms.

In the semiconductor, the doping level due to impurity implantation is formed between the valence band and the conduction band. The p-type impurity level is formed near the valence band and the n-type level is formed near the conduction band.

As shown in FIG. 13, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) can be displayed in the energy band structure of the graphene quantum dot, respectively. The absorption and the optical luminescence spectrum corresponding to the energy gap between HOMO and LUMO are observed by the electron transition.

Therefore, in Fig. 14, the absorption spectrum of the quantum dot (absorption peak is 300 nm) corresponds to the transition between electrons occurring between HOMO and LUMO. When N is doped into the quantum dot, a new impurity level is generated between HOMO and LUMO.

As shown in the EELS results, the energy level generated by the combination of CN / C = N is N π *, and a new absorption peak associated with the absorption of N π * is observed at 354 nm along with the absorption peak before doping (300 nm) .

Since the graphene quantum dots are n-type semiconductors as shown in the Raman analysis results, the N π * impurity level exists near the LUMO that can easily transfer electrons to the LUMO, and the absorption peak observed at 354 nm is HOMO It is related to the electron transfer between N π *.

N valence Doped Grapina Optical luminescence  And Optical luminescence  life span

15 is a graph of a luminous luminescence of graphene quantum dots doped with N atoms. 16 is a graph of the optical luminescence lifetime of graphene quantum dots doped with N atoms.

The electrons transferred between the HOMO and LUMO of the graphene quantum dot recombine with HOMO holes and exhibit photoluminescence (PL), and a PL peak is observed at 418 nm as shown in FIG. After N doping, electrons trapped in LUMO with N π * level are recombined with holes in HOMO together with the electrons transferred from HOMO to the newly generated N π * energy level. Therefore, a new PL peak Is expected.

As shown in FIG. 15, after doping, the PL peak shifts 15 nm in comparison with that before doping. Also, after doping, the electrons are trapped at the N impurity level in the LUMO and then recombined with the holes, so that the PL lifetime becomes longer as shown in Fig. 16 as compared with before doping.

According to the above results, carbon and nitrogen bonds can be formed at the edges of graphene quantum dots by hydrazine treatment based on the structural and luminescent characteristics. In the case of CN / C = N bonds, graphene quantum dots are n-type semiconducting But also the absorption and emission energy can be controlled.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (14)

Mixing a bare graphene quantum dot with deionized water to produce a beaglephene quantum dot aqueous solution;
Adding hydrazine (N ₂ H ₄ ) to the aqueous solution of the bare graphene quantum dots to prepare a hydrazine mixed solution; And
Reacting the hydrazine mixed solution at a temperature of 30 to 180 ° C for 10 to 24 hours;
Lt; RTI ID = 0.0 &gt; n-type &lt; / RTI &gt; graphene quantum dot. delete The method according to claim 1,
Wherein the hydrazine is a hydrazine monohydrate. delete The method according to claim 1,
The bare graphene quantum dot is prepared by preparing a graphene oxide sheet from graphite, making a dispersion through a chemical process in which graphene oxide is repeatedly oxidized, reduced, and heat treated, and then coated on a substrate Method for producing n - type graphene quantum dot. 6. The method of claim 5,
A method for fabricating an n-type graphene quantum dot, wherein the graphene quantum dot is uniformly sized and filtered by filtering using a nanopore membrane. delete delete delete delete delete delete delete delete

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