KR20230131989A - Control method of surface properties of carbon quantum dots - Google Patents

Abstract

The present invention relates to a method for controlling the surface properties of carbon quantum dots. The method for controlling the surface properties of carbon quantum dots according to the present invention controls the surface properties of carbon quantum dots by reacting carbon quantum dots with an isocyanate group. That is, the isocyanate of the isocyanate group combines with the oxygen functional group of the carbon quantum dot to modify the surface of the carbon quantum dot, thereby controlling the wettability, solubility, and luminescence characteristics of the carbon quantum dot.

Description

{Control method of surface properties of carbon quantum dots}

The present invention relates to a method of controlling the surface properties of carbon quantum dots, and more specifically, to a method of controlling the surface properties of carbon quantum dots using an isocyanate group.

Quantum dots are materials with a crystal structure several nanometers in size and are composed of hundreds to thousands of atoms. This small-sized material has a large surface area per unit volume, so most atoms exist on the surface, and it exhibits quantum confinement effects, resulting in unique electrical, magnetic, and optical properties that are different from the inherent characteristics of the material itself. , it has chemical and mechanical properties.

Even if quantum dots are made of the same material, the color of light they emit can vary depending on the size of the particle. The smaller the particle size, the shorter the wavelength of fluorescence, and as the particle size increases, the wavelength moves to the longer wavelength region. In the case of semiconductor-based quantum dots, the extinction coefficient is 100 to 1,000 times larger than that of general organic fluorescent materials and the quantum efficiency is high, producing very strong fluorescence. Due to these characteristics, quantum dots are attracting attention as next-generation high-brightness light-emitting diodes, biosensors, lasers, and solar cell nanomaterials.

Semiconductor quantum dots are widely used in the bio-imaging field because they enable long-term monitoring and have a constant emission wavelength. However, most of them use toxic heavy metal materials as core materials, so their use is limited despite their excellent properties.

In order to solve these problems of semiconductor quantum dots, research on non-toxic, non-toxic fluorescent materials is being attempted. As an example, carbon quantum dots with excellent physical properties such as dispersibility in aqueous solutions, chemical inertness, and low photobleaching properties are being introduced.

Carbon quantum dots exhibit unique fluorescence properties similar to inorganic quantum dots. In addition, carbon quantum dots have very high hydrophilicity due to numerous oxygen functional groups located on the surface, such as hydroxyl group and carboxylic acid group. Due to the hydrophilic nature of carbon quantum dots, there is a limit to their miscibility with the polymer matrix when complexed with a hydrophobic polymer.

Therefore, surface modification methods for controlling the surface properties of carbon quantum dots include a hydrophilic oxygen functional group density control method through a thermal reduction method and a chemical modification method using a hydrophobic surface modification compound.

First, the thermal reduction method has the disadvantage of being carried out at a relatively high temperature (~150 degrees) and having limitations in hydrophobizing carbon quantum dots.

Next, in the case of a chemical modification method, a hydrophobic surface modifier having an amine group (NH ₂ ) or carboxylic acid group is reacted with the oxygen functional group of the carbon quantum dot through a covalent bond using a coupling agent. N,N'-dicyclohexyl-carbodiimide (DCC) or 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) are used as coupling agents. However, the chemical modification method has the disadvantage that it is difficult to completely remove the coupling agent remaining after the reaction.

Registered Patent Publication No. 10-2143276 (registered on 2020.08.04)

Therefore, the purpose of the present invention is to provide a method for controlling the surface properties of carbon quantum dots, which has a relatively low reaction temperature and controls the surface properties of carbon quantum dots without using a catalyst.

Another object of the present invention is to provide a method for controlling the surface properties of carbon quantum dots by controlling the wettability of the carbon quantum dots.

Another object of the present invention is to provide a method for controlling the surface properties of carbon quantum dots by controlling the solubility of the carbon quantum dots.

Another object of the present invention is to provide a method of controlling the surface properties of carbon quantum dots to control the luminescence properties of the carbon quantum dots.

In order to achieve the above object, the present invention provides a method for controlling the surface properties of carbon quantum dots, characterized in that the surface properties of the carbon quantum dots are controlled by reacting the carbon quantum dots with an isocyanate group.

The carbon quantum dots include an oxygen functional group on the surface, and the isocyanate group of the isocyanate group is combined with the oxygen functional group to control the wettability of the carbon quantum dots.

The isocyanate group may include hexyl isocyanate, benzyl isocyanate, or alkyl isocyanate.

The oxygen functional group includes a hydroxyl group and a carboxylic acid group, and when hexyl isocyanate is used as the isocyanate group, the hexyl isocyanate reacts with the oxygen functional group to form urethane. ) and forms a urea linkage.

The reaction proceeds below 100°C.

The wettability of the carbon quantum dots can be controlled by adjusting the amount of the isocyanate group added.

Before reacting with the isocyanate group, the carbon quantum dots have hydrophilicity, and as the amount of the isocyanate group increases, the wettability of the carbon quantum dots changes in the order of hydrophilic, amphiphilic, and hydrophobic.

The solubility of carbon quantum dots reacted using benzyl isocyanate as the isocyanate group in styrene increases as the amount of benzyl isocyanate added increases.

Carbon quantum dots with controlled wettability can be used as an emulsifier.

The carbon quantum dots include an oxygen functional group on the surface, and the isocyanate group of the isocyanate group is combined with the oxygen functional group to control the light-emitting characteristics of the carbon quantum dots.

As the amount of the isocyanate group increases, the PL emission maximum peak wavelength of the carbon quantum dots blue shifts.

The present invention provides a method for controlling the surface properties of carbon quantum dots, characterized in that the surface properties of carbon quantum dots are controlled by reacting the carbon quantum dots with an isocyanate group by introducing a dibutyltin dilaurate series catalyst. do.

According to the present invention, the wettability, solubility, and luminescence properties of carbon quantum dots can be improved by controlling the surface properties of carbon quantum dots using isocyanate groups.

Since the isocyanate group reacts with the oxygen functional group of the carbon quantum dot to modify the surface of the carbon quantum dot, the wettability of the carbon quantum dot can be controlled by adjusting the amount of isocyanate group added to control the surface properties.

Since the present invention uses an isocyanate group to control the surface properties of carbon quantum dots, the reaction temperature is relatively low and the surface properties of carbon quantum dots can be controlled without using a catalyst. For this reason, the method for controlling the surface properties of carbon quantum dots according to the present invention can be used to control the surface properties of large quantities of carbon quantum dots.

Carbon quantum dots with controlled wettability according to the present invention can control solubility in styrene.

Since the carbon quantum dots with controlled wettability according to the present invention can be placed at the interface between a hydrophobic oil layer and a hydrophilic water layer, they can be used as an emulsifier.

And because the isocyanate group reacts with the oxygen functional group of the carbon quantum dots, the luminescent properties of the carbon quantum dots can be controlled. That is, by adjusting the amount of isocyanate group added, the light-emitting properties of carbon quantum dots can be controlled. For example, as the amount of isocyanate groups introduced to the surface of carbon protons increases, the PL emission maximum peak wavelength blue shifts.

Figure 1 is a diagram showing a method of controlling surface properties of carbon quantum dots according to the present invention.
Figure 2 is a photograph showing the change in solubility of carbon quantum dots according to the reaction amount of hexyl isocyanate according to Example 1.
Figure 3 is a photograph showing the change in solubility of carbon quantum dots according to the reaction amount of benzyl isocyanate according to Example 2.
Figure 4 is a graph showing the results of stabilizing styrene-in-water emulsion by controlling the concentration of carbon quantum dots surface-modified with hexyl isocyanate according to Example 1.
Figure 5 is a graph showing the luminescence characteristics of carbon quantum dots according to the reaction amount of hexyl isocyanate according to Example 1.

It should be noted that in the following description, only the parts necessary to understand the embodiments of the present invention will be described, and descriptions of other parts will be omitted without departing from the gist of the present invention.

The terms or words used in the specification and claims described below should not be construed as limited to their usual or dictionary meanings, and the inventor should use the concept of terminology appropriately to explain his/her invention in the best way. It must be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined clearly. Therefore, the embodiments described in this specification and the configurations shown in the drawings are only preferred embodiments of the present invention, and do not represent the entire technical idea of the present invention, and therefore, various equivalents can be substituted for them at the time of filing the present application. It should be understood that there may be variations.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the attached drawings.

Figure 1 is a diagram showing a method of controlling surface properties of carbon quantum dots according to the present invention.

Referring to Figure 1, the method for controlling the surface properties of carbon quantum dots 10 according to the present invention controls the surface properties of the carbon quantum dots 10 by reacting the carbon quantum dots 10 with an isocyanate group. That is, the carbon quantum dots 10 include oxygen functional groups 13 on the surface. The isocyanate group 20 of the isocyanate group combines with the oxygen functional group 13 of the carbon quantum dot 10 to modify the surface of the carbon quantum dot 10, thereby controlling the surface properties of the carbon quantum dot 10. The surface properties of the carbon quantum dots 10 controlled here may include wettability, solubility in styrene, and luminescent properties.

Here, the carbon quantum dots 10 can be synthesized using a top down approach or a bottom up approach. The top-down approach is a method of synthesizing carbon positive and low points (10) by splitting them from carbon nanomaterials such as carbon black, activated carbon, or graphene. The bottom up approach is a method of synthesizing carbon quantum dots (10) from single molecules or polymers such as citric acid.

Carbon quantum dots 10 manufactured by this synthetic method exhibit strong hydrophilic properties due to oxygen functional groups 13 located on the surface, such as hydroxyl groups and carboxylic acid groups.

By surface modifying the hydrophilic carbon quantum dots 10 with isocyanate groups, the wettability of the carbon quantum dots 10 can be controlled.

The isocyanate group is a compound containing an isocyanate group (20), and includes, for example, hexyl isocyanate, benzyl isocyanate, or alkyl isocyanate, but is not limited thereto.

Figure 1 shows the process of modifying the surface of carbon quantum dots 10 using hexyl isocyanate. Oxygen functional groups (13) can be confirmed on the surface of the carbon quantum dots (10) before surface modification. According to the addition of hexyl isocyanate, the isocyanate group (20) of hexyl isocyanate is bonded to the oxygen functional group (13) on the surface of the carbon quantum dot (10). As the reaction time progresses, the number of isocyanate groups (20) bonded to the oxygen functional groups (13) increases.

Here, the surface modification reaction of the carbon quantum dots 10 using hexyl isocyanate was carried out for 24 hours in a dimethylformamide solvent at 100°C or lower without using a coupling agent or catalyst.

The isocyanate group (20) of hexyl isocyanate reacts with the oxygen functional group (13) to form a urethane and urea linkage.

As the amount of the isocyanate group 20 bonded to the oxygen functional group 13 of the carbon quantum dots 10 increases, the wettability of the carbon quantum dots 10 changes. That is, the carbon quantum dots 10 can change from initial hydrophilicity to hydrophobicity.

The isocyanate group can modify the surface of the carbon quantum dots 10 without using a coupling agent or catalyst at a low temperature of 100°C or lower. For this reason, the method for controlling the surface properties of carbon quantum dots 10 according to the present invention has the advantage of modifying the surface of a large amount of carbon quantum dots 10.

Of course, when modifying the surface of the carbon quantum dots 10 using an isocyanate group, a dibutyltin dilaurate-based catalyst can be introduced. When introducing a catalyst, the reaction temperature can be lowered and the reaction time can be shortened.

Figure 2 is a photograph showing the change in solubility of carbon quantum dots according to the reaction amount of hexyl isocyanate according to Example 1.

Referring to Figure 2, in Example 1, the surface of carbon quantum dots was modified with hexyl isocyanate. By controlling the amount of hexyl isocyanate that reacts with the oxygen functional group of the carbon quantum dots, the wettability of the carbon quantum dots can be precisely controlled.

Carbon quantum dots (pristine CDs), which have not reacted at all with hexyl isocyanate, dissolve only in the water layer in a mixture of water and the organic solvent chloroform due to their strong hydrophilicity.

As the amount of hexyl isocyanate added to the mixture increases from CD-H1 -> CD-H2 -> CD-H3 -> CD-H4, the carbon quantum dots change from hydrophilic to amphiphilic to hydrophobic. ) The wettability changes in this order.

And in the case of CD-H4, it can be seen that it was completely dissolved only in the hydrophobic chloroform layer.

Meanwhile, when using an alkyl isocyanate longer than hexyl isocyanate, the surface can be modified into carbon quantum dots with stronger hydrophobicity.

Figure 3 is a photograph showing the change in solubility of carbon quantum dots according to the reaction amount of benzyl isocyanate according to Example 2.

Referring to Figure 3, in Example 2, the surface of carbon quantum dots was modified with benzyl isocyanate. By controlling the amount of hexyl isocyanate that reacts with the oxygen functional group of the carbon quantum dots, the solubility of the carbon quantum dots in styrene can be precisely controlled.

Prepare carbon quantum dots (NS-CD-B1) that are insoluble in styrene.

Next, when benzyl isocyanate is added to the carbon quantum dots (NS-CD-B1) and reacted, it can be confirmed that the carbon quantum dots (NS-CD-B2) are dissolved in styrene depending on the amount of benzyl isocyanate added.

In other words, it can be confirmed that by increasing the amount of Belzyl isocyanate, the solubility of carbon quantum dots in styrene increases and a homogeneous solution is created.

Figure 4 is a graph showing the results of stabilizing styrene-in-water emulsion by controlling the concentration of carbon quantum dots surface-modified with hexyl isocyanate according to Example 1.

Referring to Figure 4, it is possible to place carbon quantum dots with improved wettability using isocyanate groups at the interface between a hydrophobic oil layer and a hydrophilic water layer.

Using these properties, surface-modified carbon quantum dots can be used as an emulsifier. That is, carbon quantum dots can be used as a Pickering emulsifier located at the interface between styrene and water by reacting with hexyl isocyanate and surface modifying it into carbon quantum dots with amphiphilic wettability.

And by controlling the concentration of carbon quantum dots, the size of the styrene-in-water emulsion droplet can be adjusted. That is, as the temperature of the carbon quantum dots increases, the size of the emulsified droplets decreases. Here, the concentrations of carbon quantum dots in Figures 4(a), 4(b), 4(c), and 4(d) are 0.1 wt%, 0.3 wt%, 0.5 wt%, and 1.0 wt%, respectively.

Meanwhile, Figure 4 shows that the surface-modified carbon quantum dots according to Example 1 can be used as a Pickering emulsifier by using styrene as the organic solvent, but the organic solvent is not limited to styrene. For example, in addition to styrene, organic solvents such as chloroform, dichloromethane, toluene, benzene, methyl methacrylate, etc. can be used, but are not limited to these. .

Figure 5 is a graph showing the luminescence characteristics of carbon quantum dots according to the reaction amount of hexyl isocyanate according to Example 1.

Referring to FIG. 5, PL (photoluminescence) emission, one of the optical properties of carbon quantum dots, can be additionally controlled through the reaction between oxygen functional groups and isocyanate groups on the surface of carbon quantum dots. In other words, as the isocyanate group of hexyl isocyanate introduced to the surface of the carbon quantum dot increases, the oxygen functional group decreases, so it can be seen that the PL emission maximum peak wavelength blue shifts.

In this way, PL emission characteristics can be controlled by controlling the amount of hexyl isocyanate added to the carbon quantum dots.

Meanwhile, the embodiments disclosed in the specification and drawings are merely provided as specific examples to aid understanding, and are not intended to limit the scope of the present invention. It is obvious to those skilled in the art that in addition to the embodiments disclosed herein, other modifications based on the technical idea of the present invention can be implemented.

10: Carbon quantum dot
13: Oxygen functional group
20: isocyanate group

Claims (12)

A method of controlling the surface properties of carbon quantum dots, characterized in that the surface properties of the carbon quantum dots are controlled by reacting the carbon quantum dots with an isocyanate group. According to paragraph 1,
The carbon quantum dots contain oxygen functional groups on the surface,
A method for controlling the surface properties of carbon quantum dots, characterized in that the isocyanate group of the isocyanate group is combined with the oxygen functional group to control the wettability of the carbon quantum dots. According to paragraph 2,
A method for controlling the surface properties of carbon quantum dots, wherein the isocyanate group includes hexyl isocyanate, benzyl isocyanate, or alkyl isocyanate. According to paragraph 2,
The oxygen functional group includes a hydroxyl group and a carboxylic acid group,
When hexyl isocyanate is used as the isocyanate group, the hexyl isocyanate reacts with the oxygen functional group to form a urethane and urea linkage. A method of controlling the surface properties of carbon quantum dots. . According to paragraph 4,
A method of controlling the surface properties of carbon quantum dots, characterized in that the reaction proceeds at 100°C or lower. According to paragraph 2,
A method for controlling the surface properties of carbon quantum dots, characterized in that the wettability of the carbon quantum dots is controlled by adjusting the amount of the isocyanate group added. According to clause 6,
Before reacting with the isocyanate group, the carbon quantum dots have hydrophilicity,
As the amount of the isocyanate group increases, the wettability of the carbon quantum dots changes in the order of hydrophilic, amphiphilic, and hydrophobic. According to paragraph 2,
Carbon quantum dots reacted with benzyl isocyanate as the isocyanate group are characterized in that the solubility of styrene increases as the amount of benzyl isocyanate added increases. Method for controlling surface properties of carbon quantum dots . According to paragraph 2,
A method of controlling the surface properties of carbon quantum dots, characterized in that carbon quantum dots with controlled wettability can be used as an emulsifier. According to paragraph 1,
The carbon quantum dots contain oxygen functional groups on the surface,
A method for controlling the surface properties of carbon quantum dots, characterized in that the isocyanate group of the isocyanate group is combined with the oxygen functional group to control the luminescence characteristics of the carbon quantum dots. According to clause 10,
As the amount of the isocyanate group increases, the PL emission maximum peak wavelength of the carbon quantum dots blue shifts. A method of controlling the surface properties of carbon quantum dots, characterized in that the surface properties of carbon quantum dots are controlled by introducing a dibutyltin dilaurate series catalyst to react the carbon quantum dots with an isocyanate group.