WO2020045466A1

WO2020045466A1 - Method for producing photoluminescent nanocarbon

Info

Publication number: WO2020045466A1
Application number: PCT/JP2019/033620
Authority: WO
Inventors: 忠之伊左治; 一利小高; 祐介比江嶋; 直希酒井
Original assignee: 日産化学株式会社; 国立大学法人金沢大学
Priority date: 2018-08-31
Filing date: 2019-08-28
Publication date: 2020-03-05
Also published as: TW202023939A; JP2021183548A

Abstract

A method for producing a photoluminescent nanocarbon, comprising a reaction step of reacting a raw material solution containing a carbon source compound and a nitrogen source compound, wherein a mixed solvent comprising at least two types of solvents is used as a solvent for the raw material solution. It becomes possible to produce photoluminescent nanocarbons having different exciting/emission wavelengths from each other systematically and with high efficiency by varying the contents of the components in the mixed solvent.

Description

Method for producing luminescent nanocarbon

The present invention relates to a method for producing luminescent nanocarbon synthesized from a carbon source compound and a nitrogen source compound as raw materials.

(4) Luminescent nanocarbon (carbon dots) is a new carbon nanomaterial recently discovered in soot, and has a characteristic of exhibiting strong luminescence, unlike graphene and other nanocarbon materials. In addition, organic molecules are used as the carbon source compound, and highly toxic cadmium compounds such as cadmium sulfide (CdS) and cadmium selenide (CdSe) such as semiconductor quantum dots and rare metals such as europium are used as raw materials. Not used. For this reason, luminescent nanocarbon has been attracting attention as a new luminescent material that can be used as a substitute for semiconductor quantum dots that are toxic. In recent years, various reports have been made on a method for synthesizing luminescent nanocarbon (for example, Patent Document 1).

光学 As described in Patent Document 1, the optical properties of the luminescent nanocarbon, such as the excitation and emission wavelengths, are affected by the composition of the raw material and the reaction temperature. For this reason, when producing luminescent nanocarbons, generally, the optical properties of a plurality of luminescent nanocarbons synthesized by changing the composition of the raw materials are measured, and the raw materials are manufactured so as to obtain luminescent nanocarbons having desired optical properties. A method of adjusting the composition is used.

JP 2017-43539 A

However, it is not easy to control the optical properties of the luminescent nanocarbon by changing the composition of the raw materials to obtain desired optical properties. For this reason, conventionally, it is necessary to screen the raw material every time the use or required characteristics change, and there is a problem that it takes a lot of time and cost to produce a luminescent nanocarbon having desired optical characteristics. there were.
Therefore, an object of the present invention is to provide a manufacturing method capable of efficiently obtaining luminescent nanocarbon having desired optical characteristics.

The present invention is based on the finding that luminescent nanocarbons having different optical characteristics such as excitation and emission wavelengths can be obtained by changing the solvent instead of the raw material in the raw material solution, and has the following configuration.

A method for producing a luminescent nanocarbon comprising a reaction step of reacting a raw material solution containing a carbon source compound and a nitrogen source compound, wherein the solvent of the raw material solution is a mixed solvent containing two or more solvents. Production method.
The mixed solvent preferably contains water, a mixed solvent of water and an amide compound, a mixed solvent of water and an alcohol compound, a mixed solvent of water and dimethyl sulfoxide, or water and acetonitrile And a mixed solvent consisting of

In a luminescent nanocarbon production method comprising a reaction step of reacting a raw material solution containing a carbon source compound and a nitrogen source compound, by changing the solvent in the raw material solution in the reaction step, a plurality of luminescent nanocarbons A method for producing a luminescent nanocarbon, which comprises producing, evaluating the luminescent properties of the plurality of luminescent nanocarbons, and adjusting the luminescent properties of the luminescent nanocarbon.

According to the method for producing luminescent nanocarbon of the present invention, by changing the solvent in the raw material solution, without changing the type of the carbon source compound and the nitrogen source compound, the luminescent nanocarbon having different optical characteristics such as excitation and emission wavelengths Carbon is obtained. When a mixed solvent obtained by mixing a plurality of types of solvents is used, the ratio of components can be adjusted to produce a luminescent nanocarbon having desired optical characteristics. Therefore, since it is not necessary to screen the carbon source compound and the nitrogen source compound for adjusting the optical properties, it is possible to efficiently produce the luminescent nanocarbon having the desired optical properties.

Graph of absorption spectrum of aqueous dispersion of luminescent nanocarbon (a) Example 1, (b) Example 2, (c) Example 3, (d) Example 4, (e) Example 5, (f) Example 6 Graph of contour plot obtained by measurement of excitation / emission spectrum of luminescent nanocarbon (a) Example 1, (b) Example 2, (c) Example 3, (d) Example 4, (e) Example 5, (f) Example 6 The graph which shows the absorption spectrum of the water dispersion liquid of the light emitting nanocarbon of Examples 7-1 to 7-9 using the mixed solvent of DMF and water. Graphs of contour plots obtained by excitation / emission spectrum measurement of luminescent nanocarbon using a mixed solvent of DMF and water (a) Example 7-1, (b) Example 7-2, (c) execution Example 7-3, (d) Example 7-4, (e) Example 7-5, (f) Example 7-6, (g) Example 7-7, (h) Example 7-8, (I) Example 7-9 Graph showing FT-IR spectrum measurement results of luminescent nanocarbon using a mixed solvent of DMF and water Graph showing the absorption spectrum of an aqueous dispersion of luminescent nanocarbon using a mixed solvent of methanol and water Graphs of contour plots obtained by excitation / emission spectrum measurement of luminescent nanocarbon using a mixed solvent of methanol and water (a) Example 8-1, (b) Example 8-2, (c) Example 8-3, (d) Example 8-4, (e) Example 8-5, (f) Example 8-6, (g) Example 8-7, (h) Example 8-8, (I) Example 8-9, (j) Example 8-10 Graph showing FT-IR spectrum measurement results of luminescent nanocarbon using a mixed solvent of methanol and water Graph showing the absorption spectrum of an aqueous dispersion of luminescent nanocarbon using a mixed solvent of NMP and water Graphs of contour plots obtained by excitation / emission spectrum measurement of luminescent nanocarbon using a mixed solvent of NMP and water (a) Example 9-1, (b) Example 9-2, (c) execution Example 9-3, (d) Example 9-4, (e) Example 9-5, (f) Example 9-6, (g) Example 9-7, (h) Example 9-8, (I) Example 9-9, (j) Example 9-10 Graph showing the absorption spectrum of an aqueous dispersion of luminescent nanocarbon using a mixed solvent of DMA and water Graphs of contour plots obtained by excitation / emission spectrum measurement of luminescent nanocarbon using a mixed solvent of DMA and water (a) Example 10-1, (b) Example 10-2, (c) Example Example 10-3, (d) Example 10-4, (e) Example 10-5, (f) Example 10-6, (g) Example 10-7, (h) Example 10-8, (I) Example 10-9, (j) Example 10-10

(Embodiment 1)
The luminescent nanocarbon production method of the present embodiment is a luminescent nanocarbon production method comprising a reaction step of reacting a raw material solution containing a carbon source compound and a nitrogen source compound, wherein two or more kinds of solvents for the raw material are used. A mixed solvent containing a solvent is used.

Examples of the solvent used as a component of the mixed solvent include N, N dimethylformamide (DMF), formamide, N-methyl-2-pyrrolidone (NMP), 1,3-dimethyl-2-imidazolidinone (DMI), N Amide compounds such as N, N-dimethylacetamide (DMA), alcohol compounds such as methanol, ethanol, 1-propanol, isopropanol, ethylene glycol and propylene glycol, dimethyl sulfoxide (DMSO), acetonitrile (AN) and water. By using a mixed solvent obtained by mixing a plurality of solvents as a solvent of a reaction solution to be reacted in the reaction step, by changing the type and ratio of the mixed solvent, efficiently producing luminescent nanocarbons having different optical characteristics. Can be.

The reaction step is performed by a solvothermal synthesis method for producing luminescent nanocarbon using a high-temperature or high-pressure solvent. When the mixed solvent contained in the raw material solution contains water, the reaction step of reacting the carbon source compound and the nitrogen source compound is hydrothermal synthesis in which the compound is synthesized in the presence of high-temperature and high-pressure water. In the hydrothermal synthesis, since the optical properties of the luminescent nanocarbon can be adjusted by changing the content of water in the mixed solvent, a mixed solvent containing water (a mixed solvent containing water) is preferable as the mixed solvent.

When the mixed solvent is composed of two components of water and another solvent, the other solvent may be N, N-dimethylformamide, formamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazo Preferred are amide compounds such as lydinone and N, N-dimethylacetamide, (lower) alcohol compounds such as methanol, ethanol, propanol, ethylene glycol and propylene glycol, dimethyl sulfoxide and acetonitrile.

By using a mixed solvent consisting of an amide compound, an alcohol compound, dimethyl sulfoxide or acetonitrile, and water, a single solvent can be used when the content of water in the mixed solvent is 0.1% by weight or more and less than 50% by weight. When used, a luminescent nanocarbon having an emission peak that is not recognized may be obtained. In this case, the emission peak disappears when the water content is 50% or more. Therefore, the emission peak can be controlled by adjusting the content of water in the mixed solvent, and the excitation / emission characteristics of the luminescent nanocarbon can be adjusted.

有機 As the carbon source compound contained in the raw material solution, organic acids such as hydroxy acids and sugar acids, sugars (glucose), polyvinyl alcohol and the like can be used. Hydroxy acids include citric acid (anhydride and monohydrate), malic acid, tartaric acid, galactaric acid (2,3,4,5-tetrahydroxyadipic acid, mucous acid), quinic acid, glyceric acid, gluconic acid , Glucuronic acid, ascorbic acid, gallic acid and the like.

窒素 As the nitrogen source compound contained in the raw material solution, an aliphatic amine, an aromatic amine, a hydroxylamine, a polyamine, an amine compound such as a heterocyclic amine, urea, or the like can be used. Examples of the aliphatic amine include monoamines such as hexylamine, and diamines such as N, N-dimethylethylenediamine and ethylenediamine. Examples of the aromatic amine include phenylenediamine.

発光 The method for producing luminescent nanocarbon of the present embodiment includes a reaction step of heating a raw material solution in a reaction vessel to cause a reaction at a temperature of 100 to 500 ° C. In the present invention, the raw material solution refers to a solution containing a carbon source compound, a nitrogen source compound and a solvent.

The reaction step is a step of heating the raw material solution in a reaction vessel in a sealed state to synthesize luminescent nanocarbon as a reaction product reacted at a reaction temperature of 100 ° C. or more and 500 ° C. or less. Preferably, the carbon source compound and the nitrogen source compound are reacted in a solvent under a condition where the raw material solution is uniformly present in the reaction vessel, that is, in the raw material solution in a uniform state at a pressure higher than the gas-liquid equilibrium. . A homogeneous state is a state in which a stationary interface between the gas phase and the liquid phase does not exist, that is, a state in which the gas phase and the liquid phase are mixed together and no interface exists, or a position where the interface exists but the interface exists. A state that is not constant but fluctuates.

For example, a state in which a raw material solution in a reaction vessel forms a supercritical phase (supercritical fluid) having both gas diffusivity and liquid solubility is an example of a uniform state in which no interface exists. . By setting the temperature in the reaction vessel at a critical temperature or higher and a critical pressure or higher, a supercritical phase of the raw material solution can be formed.

Further, when a small amount of bubbles is present in the raw material solution in the reaction vessel, this is an example of a state where the position of the interface is not constant but fluctuates. When a gas is generated due to a side reaction of the synthesis reaction of the luminescent nanocarbon or the like, a small amount of bubbles may be present in the raw material solution.

温度 The temperature in the reaction vessel (reaction temperature) in the reaction step is 100 ° C or more and 500 ° C or less. By setting the reaction temperature to 100 ° C. or higher, a hydrothermal reaction can be promoted. Further, from the viewpoint of improving the conversion rate at which the raw material solution is converted to luminescent nanocarbon in the reaction step and suppressing the generation of insoluble components having lost luminescence, the reaction temperature is more preferably set to 150 ° C. or higher, and more preferably 180 ° C. It is more preferable that the temperature be equal to or higher than ° C.

(4) The reaction temperature is generally 500 ° C. or lower, preferably 400 ° C. or lower, and more preferably 300 ° C. or lower in order to further advance the conversion reaction in the reaction step and suppress the generation of insoluble components.

(4) When the reaction step is a batch reaction (batch type), an amount of the raw material solution in the reaction vessel in which the density becomes higher than the gas-liquid equilibrium state in the reaction step is charged. Further, in the case of production by a flow-type (continuous) reaction, the reaction vessel is adjusted so that the temperature and pressure at which the raw material solution in the reaction vessel in the reaction step has a density higher than the gas-liquid equilibrium state. This allows the raw material solution in the reaction step to be in a uniform state, that is, a state in which gas and liquid are mixed together in the reaction vessel, so that the reaction can proceed efficiently. Further, it is not necessary to use a combination that forms a salt as the carbon source compound and the nitrogen source compound contained in the raw material solution. For example, it is possible to use not only raw materials that form salts such as citric acid and amines, but also combinations of raw materials that do not form salts such as glucose (glucose) and amines.

(4) The reaction vessel used in the reaction step has pressure resistance to high temperature and high pressure conditions. When the reaction step is a batch-type reaction, the entire reaction vessel in which the raw material solution is charged is heated to set the entire inside of the reaction vessel to a predetermined temperature and pressure, and the reaction step proceeds in the entire reaction vessel. For example, a tubular high-pressure vessel (autoclave) is used as a reaction vessel, and the reaction step proceeds by charging the reaction vessel into an electric furnace set at a predetermined temperature. After the completion of the reaction step, the reaction solution containing the reaction product is cooled by removing the tubular high-pressure vessel into room temperature air and air-cooling (cooling step).

When the reaction step is a batch-type (batch-type) reaction, it is preferable to charge an amount of the raw material solution having a density higher than the gas-liquid equilibrium state in the reaction vessel. For example, the saturation density of water (liquid phase), the reaction temperature 0.99 ° C., 200 ° C., at 250 ° C. and 300 ° C., this order ^{^{0.917g / cm 3, 0.864g / cm}} 3, 0.799g / cm 3 and 0.712 g / cm ³ . Therefore, when the reaction temperature is set to 200 ° C. to 250 ° C., an amount of the raw material solution that is about 90% (80% to 97%, preferably 85% to 95%) of the volume of the reaction vessel may be charged. preferable. By charging such an amount of the raw material solution, the raw material solution is present in a uniform state in the reaction step, and the reaction efficiency is improved.

場合 When the reaction step is a continuous reaction, use a pressure-resistant reaction vessel having a continuous long internal space like a long and thin tube. By heating a part of a reaction vessel having a sufficient length while supplying a raw material solution from one end of an elongated tube, a reaction step is continuously performed in a part of the reaction vessel to perform a reaction step. Can be. In the reaction step, the pressure in the reaction vessel is adjusted so that the concentration of the raw material solution becomes higher than the saturated vapor pressure at which the gas-liquid equilibrium is reached. For example, the saturated vapor pressure of water is 0.48 MPa at 150 ° C., 1.55 MPa at 200 ° C., 3.98 MPa at 250 ° C., 8.59 MPa at 300 ° C., and 16.53 MPa at 350 ° C. Is adjusted to be equal to or higher than the saturated vapor pressure at the reaction temperature. As a result, the raw material solution is present in a uniform state in the reaction step, so that the reaction efficiency is improved.

発光 By cooling the other part communicating with the part where the reaction step is performed (cooling step), luminescent nanocarbon is obtained from the reaction solution. The cooling step is performed by, for example, rapidly cooling a part of the elongated tube as the reaction vessel using an ice bath or a water bath.

When the reaction step and the cooling step are made to proceed in different parts of the reaction vessel, and the part where the reaction step proceeds and the part where the cooling step proceeds are connected, the raw material solution and the reaction solution move in the reaction vessel. By doing so, the reaction step and the cooling step proceed continuously and simultaneously.

If the reaction step is performed in a part of the region and the cooling step is performed in the other region using the above-described reaction container, the reaction step and the cooling step proceed continuously and simultaneously. Can be produced.

(Embodiment 2)
The present invention provides a method for producing a luminescent nanocarbon, comprising a reaction step of reacting a raw material solution containing a carbon source compound and a nitrogen source compound, wherein a plurality of luminescences are obtained by changing a solvent in the raw material solution in the reaction step. The method may be implemented as a method for producing a luminescent nanocarbon by producing luminescent nanocarbon, evaluating the luminescent properties of the plurality of luminescent nanocarbons, and adjusting the luminescent properties of the luminescent nanocarbon.

The present invention is based on the finding that luminescent nanocarbons having different excitation / emission wavelengths can be obtained by using different solvents in the reaction step. By performing the reaction step by changing the solvent, a plurality of luminescent nanocarbons having different emission characteristics can be produced more efficiently than by performing the reaction step by changing the carbon source compound and the nitrogen source compound.

溶媒 The solvent used for the raw material solution may be a single solvent or a mixed solvent obtained by mixing plural kinds of solvents. However, it is preferable to use a mixed solvent because a plurality of luminescent nanocarbons can be efficiently produced by changing the ratio of the components.

用いる When a mixed solvent is used, a mixed solvent containing water (a mixed solvent containing water) is preferable. By using a mixed solvent containing water, the magnitude of the emission peak may change continuously with the content of water. By using such a water-containing mixed solvent, the light emitting characteristics of the light emitting nanocarbon can be efficiently adjusted. That is, since the excitation / emission wavelength changes remarkably with a certain tendency depending on the content of water in the mixed solvent, it is possible to efficiently produce a plurality of luminescent nanocarbons having different excitation / emission wavelengths. .

評価 Evaluate the luminescent properties of a plurality of luminescent nanocarbons produced using different solvents, and adjust the luminescent properties of the luminescent nanocarbons with the solvent in the raw material solution. The method of changing the solvent in the raw material solution is easier to adjust the production conditions than the method of screening the carbon source compound and the nitrogen source compound in the raw material solution. It is possible to produce carbon efficiently.

In order to examine the effect of the solvent in the raw material solution on the optical properties of the luminescent nanocarbon, N, N dimethylformamide (DMF), Luminescent nanocarbons were produced using formamide, methanol, ethanol, 1-propanol and water, respectively. Each luminescent nanocarbon was solvothermally synthesized by a batch operation using an autoclave.

[Example 1]
Using 2 g of citric anhydride (manufactured by Sigma-Aldrich, carbon source compound), 4 g of urea (manufactured by Tokyo Chemical Industry Co., Ltd., nitrogen source compound), and 41 g of DMF (manufactured by Nacalai Tesque, Inc., solvent), 41 g A solution was prepared. 9 mL of the raw material solution was sealed in an autoclave made of SUS316 having a capacity of about 10 mL, and heated in an electric furnace at 200 ° C. for 1, 3, and 6 hours to produce luminescent nanocarbon by solvothermal synthesis.

[Example 2]
A luminescent nanocarbon was produced in the same manner as in Example 1 except that 120 g of formamide (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as a solvent instead of 41 g of DMF.
[Example 3]
A luminescent nanocarbon was produced in the same manner as in Example 1 except that 27 g of methanol (manufactured by Nacalai Tesque, Inc.) was used as a solvent instead of 41 g of DMF.

[Example 4]
The supernatant was used because 60 g of ethanol (manufactured by Nacalai Tesque, Inc.) was used as a solvent instead of 41 g of DMF, and citric anhydride and urea (hereinafter collectively referred to as “raw materials”) were not completely dissolved in the solvent. Except for this, a luminescent nanocarbon was produced in the same manner as in Example 1.

[Example 5]
A luminescent nanoparticle was prepared in the same manner as in Example 1 except that 80 g of 1-propanol (manufactured by Kanto Chemical Co., Ltd.) was used as a solvent instead of 41 g of DMF, and the supernatant was used because the raw material was not completely dissolved in the solvent. Carbon was produced.
[Example 6]
A luminescent nanocarbon was produced in the same manner as in Example 1 except that 38 g of water was used as a solvent instead of 41 g of DMF.

After collecting the synthesized luminescent nanocarbons of Examples 1 to 6, each was dried and dried in water at 0.01% by weight (Examples 1, 2, and 6) or 0.05% by weight (Examples 3, 2, and 6). Table 1 shows the results of observing the color of the dispersions dispersed in 4) and 5) under room natural light.

As shown in Table 1, when the luminescent nanocarbon was synthesized by the solvothermal method, it was found that the type of the solvent used for the raw material solution and the heating time affected the optical properties of the luminescent nanocarbon.

(Measurement of absorption spectrum)
With respect to each of the dispersions of Examples 1 to 6 in which the color was observed under room natural light, the absorption spectrum was measured using a spectrophotometer F-2700 manufactured by Hitachi High-Technologies Corporation, and the absorption characteristics of each luminescent nanocarbon were measured. Examined. In the graphs of the absorption spectra shown in FIGS. 1A to 1F, the horizontal axis indicates the wavelength (Wavelength / nm), and the vertical axis indicates the absorbance (Absorbance / −).

吸収 As shown in FIG. 1 (a), in the absorption spectrum of the luminescent nanocarbon synthesized using DMF as a solvent, broad absorption was confirmed from a wavelength of 350 nm to 550 nm. In addition, it was found that the absorbance increased as the reaction time increased.

As shown in FIG. 1 (b), in the absorption spectrum of the luminescent nanocarbon synthesized using formamide as a solvent, a strong absorption peak was confirmed at a wavelength of about 320 nm, and a weak absorption peak was also confirmed at a wavelength of about 550 nm. .

As shown in FIG. 1 (c), in the absorption spectrum of the luminescent nanocarbon synthesized using methanol as a solvent, a strong absorption peak was confirmed at a wavelength of about 330 nm, and weak absorption peaks were also found at a wavelength of about 400 nm and about 450 nm. confirmed. In addition, it was found that the absorbance decreased as the reaction time increased.

As shown in FIG. 1 (d), in the absorption spectrum of the luminescent nanocarbon synthesized using ethanol as a solvent, strong absorption peaks were observed around 350 nm and 390 nm, and a shoulder peak was also observed around 450 nm. Was done. In addition, it was found that the absorbance increased as the reaction time increased.

As shown in FIG. 1 (e), in the absorption spectrum of the luminescent nanocarbon synthesized using 1-propanol as a solvent, strong absorption peaks were observed at around 350 nm and 390 nm, and a shoulder peak was also observed at around 450 nm. Was confirmed.

As shown in FIG. 1 (f), in the absorption spectrum of the luminescent nanocarbon synthesized using water as a solvent, a strong absorption peak was confirmed at a wavelength of about 330 nm, and weak absorption peaks were also found at a wavelength of about 400 nm and about 600 nm. confirmed.

By comparing the absorption spectra shown in FIGS. 1 (a) to 1 (f), when the luminescent nanocarbon is synthesized by the solvothermal method, by changing the type of the solvent in the raw material solution, the luminescence having different chemical structures is obtained. It was suggested that conductive nanocarbon could be obtained.

(Excitation / emission spectrum measurement)
FIGS. 2A to 2F show contour plots obtained by measurement of excitation and emission spectra of the luminescent nanocarbons of Examples 1 to 6 in which the heating time of the reaction step was set to 3 hours. 3 shows a graph. In these graphs, the horizontal axis indicates the emission wavelength (Emission wavelength / nm), the vertical axis indicates the excitation wavelength (Excitation wavelength / nm), and the shading indicates the photoluminescence intensity (PL intensity).

From the graphs of FIGS. 2 (a), 2 (c), 2 (d) and 2 (e), it can be seen that the luminescent nanocarbon using DMF, methanol, ethanol and 1-propanol as solvents has an excitation wavelength of around 370 nm. It can be seen that the characteristics of the excitation and emission spectra are similar in that there is a peak near the emission wavelength of 450 nm and that emission can be confirmed even in the longer wavelength range up to the excitation wavelength of 450 nm and the emission wavelength of around 600 nm. .

On the other hand, the luminescent nanocarbon using formamide as a solvent shown in FIG. 2B has a peak at an excitation wavelength of 350 nm and an emission wavelength of about 450 nm, and emits light at an excitation wavelength of 300 nm and an emission wavelength of about 350 nm on the shorter wavelength side. It could be confirmed.

In addition, in the luminescent nanocarbon synthesized using water as a solvent shown in FIG. 2 (f), peaks near an excitation wavelength of 350 nm and an emission wavelength of 450 nm were confirmed, and it was found that the wavelength range in which luminescence was emitted was narrow.

As described above, it was found that luminescent nanocarbons having different excitation and emission characteristics can be obtained depending on the type of the solvent of the raw material solution used for the solvothermal synthesis. In particular, it was found that by using water as a solvent, a luminescent nanocarbon having characteristic excitation and emission characteristics different from those obtained when an amide compound or an alcohol compound was used was obtained.

Therefore, the solvent in the raw material solution was used as a mixed solvent consisting of multiple components, and the effect of the difference in the water content (addition rate) in the mixed solvent on the optical properties of the luminescent nanocarbon obtained by solvothermal synthesis was examined. In order to do this, a luminescent nanocarbon was produced using a mixed solvent.

[Example 7 mixed solvent (DMF + water)]
0.4 g of citric anhydride (Sigma-Aldrich, carbon source compound) and 0.8 g of urea (Tokyo Kasei Kogyo Co., Ltd., nitrogen source compound) were mixed with DMF (Nacalai Tesque, solvent, solvent). A raw material solution was prepared by adding and dissolving 10 mL of a mixed solvent with water.
9 mL of each raw material solution prepared using the mixed solvent adjusted to the water content shown in Table 2 was sealed in a SUS316 autoclave having a capacity of about 10 mL, and heated in an electric furnace at 200 ° C. for 3 hours. Luminescent nanocarbon was produced by synthesis.

Each of the manufactured luminescent nanocarbon solutions was dialyzed for about 20 hours using a regenerated cellulose semipermeable membrane (manufactured by Spectra @ Por) having a MWCO of 100 to 500 Da to remove low molecular components having a molecular weight of less than 100 to 500 Da. Pressure filtration was performed using a nylon syringe filter (manufactured by Rephile Bioscience Ltd.) to remove coarse by-products, and thus the luminescent nanocarbon was purified.

(Transmission electron microscope (TEM) observation)
The luminescent nanocarbons synthesized by solvothermal using mixed solvents having different water contents were subjected to TEM observation to examine the particle diameter. H-7650 manufactured by Hitachi High-Technologies Corporation was used for TEM observation. As the TEM grid, a TEM grid with a supporting film (manufactured by Oken Shoji Co., Ltd.) whose surface was hydrophilized by performing an arc treatment in vacuum for 2 seconds was used. As a measurement sample for TEM observation, luminescent nanocarbon before purification was used.

As a result of TEM observation, it was found that all of the luminescent nanocarbons of Examples 7-1 to 7-9 existed as spherical nanoparticles having a particle diameter of about 1 to 2 nm. Further, the luminescent nanocarbon of each example had a median diameter (d50) of 1.2 nm to 1.4 nm. From these results, it was found that the water content in the mixed solvent of DMF and water did not affect the shape and particle size of the synthesized (produced) luminescent nanocarbon.

(Measurement of absorption spectrum)
In order to examine the light absorption properties of the luminescent nanocarbons of Examples 7-1 to 7-9, each of the luminescent nanocarbons was recovered and used for 20 hours using a regenerated cellulose semipermeable membrane (manufactured by Spectra Por) having a MWCO of 100 to 500 Da. Dialysis is performed, low molecular components of less than 100-500 Da are removed, pressure filtration is performed using a nylon syringe filter (manufactured by Rephile Bioscience) having a pore size of 220 nm, and after removing coarse by-products, drying is performed. An aqueous dispersion dispersed in water at 0.01% by weight was prepared. FIG. 3 shows the results of measuring the absorption spectrum of each aqueous dispersion using a spectrophotometer F-2700 manufactured by Hitachi High-Tech Science Corporation. In the graph of the absorption spectrum shown in the figure, the horizontal axis represents wavelength (Wavelength / nm), and the vertical axis represents absorbance (Absorbance /-).

発光 As shown in FIG. 3, the peak of the absorption spectrum is observed around 340 nm and 430 nm in the luminescent nanocarbon using the mixed solvent having the water content of 0.1% by weight to 20% by weight. Among these, it was found that the peak around 430 nm shifted to the shorter wavelength side as the content of water in the mixed solvent increased. Further, it was found that when the content of water in the mixed solvent was 50% by weight or more, the peak of the absorption spectrum around 430 nm was not observed.

From these results, it can be seen that by using DMF and water as a mixed solvent, peaks of the absorption spectrum (around 430 nm, see FIGS. 1 (a) and 1 (f)) which are not remarkably recognized with each single solvent appear. , And the magnitude of the peak was found to be controllable by the water content.

(Excitation / emission spectrum measurement)
FIGS. 4A to 4I show graphs of contour plots obtained by measuring the excitation and emission spectra of the luminescent nanocarbons of Examples 7-1 to 7-9. In these graphs, the horizontal axis indicates the emission wavelength (Emission wavelength / nm), the vertical axis indicates the excitation wavelength (Excitation wavelength / nm), and the shading indicates the photoluminescence intensity (PL intensity).

(2) In the light-emitting nanocarbon synthesized using the mixed solvent having a small water content, two light emission peaks were observed at around 350 nm, around 450 nm, around 400 nm, and around 530 nm. The emission peak around 400 nm excitation and 530 nm emission (see FIGS. 4 (b) to 4 (e)), which is remarkably observed when the water content is 0.5% by weight or more and 10% by weight or less, is obtained by using DMF or water alone. (FIG. 2 (a) and FIG. 2 (f)). From this, it can be said that by using DMF and water as a mixed solvent, a luminescent nanocarbon having an excited luminescence characteristic different from the case of using each single solvent was synthesized. When the content of water in the mixed solvent is larger than 20% by weight, the emission peaks around 400 nm and 530 nm of the excitation appearing by using the mixed solvent gradually decrease as the content of water increases. It turned out to disappear. As described above, the emission peak that appears when the mixed solvent is used changes continuously and gradually as the content of water increases. Therefore, it can be said that a mixed solvent composed of DMF and water is useful for synthesizing a luminescent nanocarbon having desired excitation / emission characteristics.

(FT-IR spectrum measurement)
In order to examine the chemical structures of the luminescent nanocarbons of Examples 7-1 to 7-9, FT-IR spectrum measurement was performed by the KBr tablet method. As the measuring device, FT / IR-4200 manufactured by JASCO Corporation was used. A tablet sample for measurement was prepared by pulverizing and mixing about 0.5 mg of a dried luminescent nanocarbon sample and 50 mg (0.05 g) of KBr powder (manufactured by Kanto Chemical Co., Ltd.) in a mortar and using a simple tablet molding machine. Produced.

FIG. 5 is a graph showing FT-IR spectra of luminescent nanocarbons solvothermally synthesized in a mixed solvent of DMF and water having different water contents. The horizontal axis of the graph indicates the wave number (Wave number / cm ^-1 ). The measurement results of the FT-IR spectrum of the starting material (Starting material: citric acid + urea) are shown for comparison. As shown in the figure, as the water content in the mixed solvent increases, the peak attributable to the CH bending vibration near 1400 cm ^-1 increases, and the peak belongs to the C = O stretching vibration at 1700 cm ^-1. Peaks found to decrease. From these results, it is considered that the molecular structure was changed by changing the water content in the mixed solvent, and as a result, the luminescent properties of the synthesized luminescent nanocarbon were changed.

[Example 8 mixed solvent (methanol + water)]
Light emitting nanocarbon was synthesized using methanol instead of DMF of Example 7. For each mixed solvent of methanol and water adjusted to the water content shown in Table 3, luminescent nanocarbon was produced by solvothermal synthesis in the same manner as in Example 7.
The manufactured luminescent nanocarbon solution was purified in the same manner as in Example 7.

(Transmission electron microscope (TEM) observation)
TEM observation was performed in the same manner as in Example 7 to check the particle size of the luminescent nanocarbon. A luminescent nanocarbon before purification was used as a measurement sample.

As a result of TEM observation, it was found that all the luminescent nanocarbons of Examples 8-1 to 8-10 existed as spherical nanoparticles having a particle diameter of about 1 to 2 nm. Further, the luminescent nanocarbon of each example had a median diameter (d50) of 1.1 to 1.4 nm. From these results, it was found that changing the water content in the mixed solvent of methanol and water hardly changed the shape and particle size of the produced luminescent nanocarbon.

(Measurement of absorption spectrum)
In order to examine the light absorption properties of the luminescent nanocarbons of Examples 8-1 to 8-10, each of the luminescent nanocarbons was recovered and used for 20 hours using a regenerated cellulose semipermeable membrane (Spectra Por) having a MWCO of 100 to 500 Da. After dialysis, low molecular components of less than 100-500 Da were removed, and pressure filtration was performed using a nylon syringe filter (manufactured by Rephile Bioscience) having a pore size of 220 nm to remove coarse by-products, followed by drying. An aqueous dispersion dispersed in water at 0.025% by weight was prepared. FIG. 6 shows the results of measuring the absorption spectrum of each aqueous dispersion using a spectrophotometer F-2700 manufactured by Hitachi High-Tech Science Corporation. In the graph of the absorption spectrum shown in the figure, the horizontal axis represents wavelength (Wavelength / nm), and the vertical axis represents absorbance (Absorbance /-).

発光 As shown in FIG. 6, in the luminescent nanocarbon using the mixed solvent having a water content of 0.1% by weight, absorption spectrum peaks are observed around 340 nm and 400 nm. Of these, it was found that the peak near 400 nm gradually decreased as the content of water in the mixed solvent increased. Further, it was found that when the content of water in the mixed solvent was 50% by weight or more, an absorption peak near 400 nm was not observed.

(Excitation / emission spectrum measurement)
FIGS. 7A to 7J show graphs of contour plots obtained by measuring the excitation and emission spectra of the luminescent nanocarbons of Examples 8-1 to 8-10. In these graphs, the horizontal axis indicates the emission wavelength (Emission wavelength / nm), the vertical axis indicates the excitation wavelength (Excitation wavelength / nm), and the shading indicates the photoluminescence (PL intensity).

The luminescent nanocarbon synthesized using the mixed solvent having a small water content shows that the shape of the graph shown by the contour plot substantially coincides with the water content of 0.1% by weight to 36% by weight. Was. By using a mixed solvent having a water content within this range, it can be said that luminescent nanocarbons having substantially the same excitation / emission dependence are produced. In addition, it was found that when the content of water in the mixed solvent was 50% by weight or more, the emission at around 430 nm was enhanced by excitation with a short wavelength of 400 nm or less.

Also when using a mixed solvent of methanol and water, methanol or water alone is not remarkably observed (see FIGS. 2 (c) and 2 (f)), excitation around 400 nm, emission 530 nm. Near emission peaks were observed (see FIGS. 7A to 7G). It was found that this emission peak became smaller when the water content was 50% by weight or more.

(FT-IR spectrum measurement)
In order to examine the chemical structures of the luminescent nanocarbons of Examples 8-1 to 8-10, FT-IR spectrum measurement was performed in the same manner as in Example 7.
FIG. 8 is a graph showing FT-IR spectra of luminescent nanocarbons solvothermally synthesized in a mixed solvent of methanol and water having different water contents. The horizontal axis of the graph indicates the wave number (Wave number / cm ^-1 ). The measurement results of the FT-IR spectrum of the starting material (Starting material: citric acid + urea) are shown for comparison. As shown in the figure, as the water content in the mixed solvent is increased, peak attributed to C = O stretching vibration peak and 1700 cm ^-1 attributable to C-H bending vibration near 1400 cm ^-1 It was found that the peak attributed to the NH bending vibration at 1600 cm ^-1 decreased with increasing. From these results, it is considered that as a result of changing the molecular structure by changing the water content in the mixed solvent, luminescent nanocarbons having different optical properties were obtained.

[Example 9 mixed solvent (NMP + water)]
A luminescent nanocarbon was synthesized using N-methyl-2-pyrrolidone (NMP) instead of DMF of Example 7. For each mixed solvent of NMP and water adjusted to the water content shown in Table 4, luminescent nanocarbon was produced by solvothermal synthesis in the same manner as in Example 7. The manufactured luminescent nanocarbon solution was purified in the same manner as in Example 7.

After collecting each of the synthesized luminescent nanocarbons of Example 9-1 to Example 9-10, the color was observed under room natural light of a dispersion obtained by drying and dispersing 0.01% by weight in water. It was found that the yellowish brown color became thinner as the content of water in the mixed solvent increased. In addition, as a result of observing light emission under ultraviolet light, it was found that green light was changed to blue light as the content of water in the mixed solvent was increased.

(Measurement of absorption spectrum)
In order to examine the light absorption characteristics of the luminescent nanocarbons of Examples 9-1 to 9-10, purification was carried out in the same manner as in Example 7, and the luminescent nanocarbon was dispersed in water at 0.01% by weight in water. A liquid was prepared. FIG. 9 shows the results of measuring the absorption spectrum of each aqueous dispersion using a spectrophotometer F-2700 manufactured by Hitachi High-Tech Science Corporation. In the graph of the absorption spectrum shown in the figure, the horizontal axis represents wavelength (Wavelength / nm), and the vertical axis represents absorbance (Absorbance /-).

示す As shown in FIG. 9, in the case of a luminescent nanocarbon using a mixed solvent having a water content of 0.1% by weight to 20% by weight, absorption spectrum peaks are observed at around 340 nm, 390 nm and 450 nm. It was found that when the content of water in the mixed solvent was 50% by weight or more, the absorption peak near 340 nm increased and the absorption peak near 450 nm decreased. Further, it was found that the absorption peak near 340 nm gradually shifted to the shorter wavelength side as the water content increased.

(Excitation / emission spectrum measurement)
FIGS. 10 (a) to 10 (j) show graphs of contour plots obtained by measuring the excitation and emission spectra of the luminescent nanocarbons of Examples 9-1 to 9-10. In these graphs, the horizontal axis indicates the emission wavelength (Emission wavelength / nm), the vertical axis indicates the excitation wavelength (Excitation wavelength / nm), and the shading indicates the photoluminescence (PL intensity).

When the content of water in the mixed solvent is small, the luminescent nanocarbon synthesized using the mixed solvent having a small water content has an emission peak near 350 nm for excitation and 450 nm for emission, and also has a peak for emission near 450 nm and 520 nm for emission. It was found to emit light. As the content of water in the mixed solvent increased, the emission near the excitation of 450 nm and the emission of 520 nm gradually weakened, and it was found that almost no confirmation was possible when the content of water was 50% by weight or more.

[Example 10 mixed solvent (DMA + water)]
A luminescent nanocarbon was synthesized using N, N-dimethylacetamide (DMA) instead of DMF of Example 7. Luminescent nanocarbon was produced by solvothermal synthesis in the same manner as in Example 7 for each of the mixed solvents of DMA and water adjusted to the water contents shown in Table 5. The manufactured luminescent nanocarbon solution was purified in the same manner as in Example 7.

After collecting the synthesized luminescent nanocarbons of Examples 10-1 to 10-10, the color of the dispersions dried and dispersed in water at 0.01% by weight was observed under room natural light. It was found that the yellowish brown color became thinner as the content of water in the mixed solvent increased. In addition, as a result of observing light emission under ultraviolet light, it was found that green light was changed to blue light as the content of water in the mixed solvent was increased.

(Measurement of absorption spectrum)
In order to examine the light absorption properties of the luminescent nanocarbons of Examples 10-1 to 10-10, each of the luminescent nanocarbons was recovered, purified by the same method as in Example 7, and the luminescent nanocarbon was dissolved in water at a concentration of 0.1 mM. An aqueous dispersion dispersed at 01% by weight was prepared. FIG. 11 shows the results of measuring the absorption spectrum of each aqueous dispersion using a spectrophotometer F-2700 manufactured by Hitachi High-Tech Science Corporation. In the graph of the absorption spectrum shown in the figure, the horizontal axis represents wavelength (Wavelength / nm), and the vertical axis represents absorbance (Absorbance /-).

示す As shown in FIG. 11, in the luminescent nanocarbon using the mixed solvent having a water content of 0.1% by weight to 20% by weight, absorption spectrum peaks are observed around 340 nm and 410 nm. It was found that when the content of water in the mixed solvent was 50% by weight or more, the peak around 340 nm increased and the peak around 410 nm decreased. Further, it was found that the peak around 340 nm gradually shifted to the shorter wavelength side as the water content increased.

(Excitation / emission spectrum measurement)
FIGS. 12A to 12J show graphs of contour plots obtained by measuring the excitation and emission spectra of the luminescent nanocarbons of Examples 10-1 to 10-10. In these graphs, the horizontal axis indicates the emission wavelength (Emission wavelength / nm), the vertical axis indicates the excitation wavelength (Excitation wavelength / nm), and the shading indicates the photoluminescence (PL intensity).

The luminescent nanocarbon synthesized using the mixed solvent having a small water content has an emission peak at around 350 nm and around 450 nm in the example having a low concentration of water in the solvent, and also at around around 450 nm and around 520 nm. It was found to emit light. It was found that the light emission near the excitation of 450 nm and the light emission of 520 nm gradually weakened as the water content in the solvent increased, and was hardly confirmed when the water content was 50% by weight or more.

The present invention can be used as a method for producing luminescent nanocarbon used for lighting, displays, optical communication devices, fluorescent probes for living organisms that require low toxicity, and the like.

Claims

A method for producing a luminescent nanocarbon comprising a reaction step of reacting a raw material solution containing a carbon source compound and a nitrogen source compound,
A method for producing a luminescent nanocarbon, wherein the solvent of the raw material solution is a mixed solvent containing two or more solvents.
The mixed solvent contains water,
The method for producing luminescent nanocarbon according to claim 1.
The mixed solvent is a mixed solvent of water and an amide compound, a mixed solvent of water and an alcohol compound, a mixed solvent of water and dimethyl sulfoxide, or a mixed solvent of water and acetonitrile.
The method for producing luminescent nanocarbon according to claim 1.
The amide compound is N, N dimethylformamide, N-methyl-2-pyrrolidone or N, N-dimethylacetamide;
The alcohol compound is methanol,
The method for producing a luminescent nanocarbon according to claim 3.
The method for producing luminescent nanocarbon according to any one of claims 1 to 4, wherein the carbon source compound is citric acid, and the nitrogen source compound is urea.
The reaction step synthesizes a luminescent nanocarbon by a solvothermal synthesis method,
The method for producing a luminescent nanocarbon according to any one of claims 1 to 5.
A method for producing a luminescent nanocarbon comprising a reaction step of reacting a raw material solution containing a carbon source compound and a nitrogen source compound in a reaction vessel,
By varying the solvent in the raw material solution in the reaction step, to produce a plurality of luminescent nanocarbon,
Evaluate the luminescent properties of the plurality of luminescent nanocarbons,
A method for producing a luminescent nanocarbon, comprising adjusting the luminescent properties of the luminescent nanocarbon.
The solvent in the raw material solution is a mixed solvent containing water,
By varying the content of water in the mixed solvent in the reaction step, to produce a plurality of luminescent nanocarbon,
A method for producing a luminescent nanocarbon according to claim 7.
The solvent in the raw material solution is a mixed solvent of water and N, N-dimethylformamide, a mixed solvent of water and N-methyl-2-pyrrolidone, and a mixed solvent of water and N, N-dimethylacetamide Or a mixed solvent consisting of water and methanol,
Assuming that the content of water in the mixed solvent in the reaction step is less than 50% by weight, a luminescent nanocarbon having an emission peak around 400 nm and emission around 530 nm is synthesized.
Assuming that the content of water in the mixed solvent in the reaction step is 50% by weight or more, a luminescent nanocarbon having no emission peak near 400 nm in excitation and about 530 nm in emission is synthesized.
A method for producing a luminescent nanocarbon according to claim 8.