KR20170091886A - Preparing method of two dimensional material dispersion, and ink including two dimensional material dispersion - Google Patents

Abstract

The present invention relates to a method for producing a two-dimensional material dispersion, and an ink including a two-dimensional material dispersion thereof. The method for producing a two-dimensional material dispersion of the present invention comprises a step of peeling and dispersing a two-dimensional material by ultrasonic treatment after adding the two-dimensional material to a solvent having micro-bubbles removed therefrom. The two-dimensional material includes graphene, boron nitride (h-BN), metal decalcogenide, bismuth strontium calcium copperoxide (BSCCO), CdTe, GaS, GaSe, GaS_(1-x)Se_x, CdI_2, PbI_2, K_2Al_4(Si_6Al_2O_28)(OH,F)_4, or Mg_6(Si_8O_28)(OH)_4. According to the present invention, a two-dimensional material dispersion can be massively produced, and is cost-effective. Also, the two-dimensional material dispersion can be readily applied as an ink in ink jet printing.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a two-dimensional material dispersion, and an ink including the two-dimensional material dispersion,

The present invention relates to a process for producing a two-dimensional material dispersion and to an ink comprising the two-dimensional material dispersion.

Methods for the synthesis of two-dimensional (2D) materials such as graphene, hexagonal boron nitride (h-BN) and MoS ₂ have been the subject of intensive research due to their excellent mechanical, electrical, optical and chemical properties . Among these synthetic methods, the method of peeling from a bulk layered material by using a chemical solvent has been widely used because of its potential to enable mass production for practical application. Many solvents have been tested for delamination and dispersion of 2D materials, but water has rarely been studied, except in the case of graphene oxide, which is very well dispersed in water due to the surface functionalities and hydrophilic properties of the water. Graphene itself can not readily dissolve in water without the presence of surface functional groups in combination with the use of surfactants or pH control. Other 2D materials have rarely been tested for dissolution in water, perhaps because of previous reports relating to the insolubility of graphene [A. Ciesielski, P. Samori, Graphene via sonication assisted liquid-phase exfoliation. Chemical Society reviews 43, 381-398 (2014)]. However, the use of pure water that does not contain any other compounds or surfactants is advantageous for the synthesis and dispersion of 2D materials, because they are cost-effective and environmentally friendly. That is, it does not involve the release of waste compounds during mass production. In addition, water-dispersed 2D materials can be used in many fields that require aquatic environments such as biology or medical research.

The present application is directed to a method for producing a two-dimensional material dispersion, and an ink containing the two-dimensional material dispersion.

However, the problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

A first aspect of the present invention provides a method of producing a two-dimensional material dispersion, comprising adding a two-dimensional material to a solvent from which microbubbles have been removed and then separating and dispersing the two-dimensional material by ultrasonic treatment.

A second aspect of the invention provides an ink comprising a two-dimensional material dispersion prepared according to the method of the first aspect of the present application.

The method of producing a two-dimensional material dispersion according to an embodiment of the present invention can synthesize a two-dimensional material having excellent dispersion stability in the solvent by using water from which fine bubbles have been removed as a solvent, This is possible and economical. In addition, the method of preparing a two-dimensional material dispersion according to one embodiment of the present invention minimizes the absorption of energy during the passage of water through ultrasonic waves by removing microbubbles present in the solvent without the use of additional compounds or surfactants It is easy to disperse and peel off graphene or other two-dimensional materials in the solvent.

Since the method of producing a two-dimensional material dispersion according to an embodiment of the present invention has little ultrasonic energy to be lost upon dispersion and separation of a two-dimensional material by a solvent from which microbubbles have been removed, No process is required.

Further, in one embodiment of the invention, the 2D material dispersion can be readily applied as an ink in ink jet printing.

1 (a) and 1 (b) are graphs showing the stability of water according to an embodiment of the present invention in water in which micro-bubbles of MoSe ₂ (black square) and WS ₂ .
Figure 2 shows the FT-IR spectrum of the 2D material in one embodiment of the invention.
Figures 3 (a) - (h) show the Raman spectra of the exfoliated material and the raw material, respectively, in one embodiment of the invention.
Figs. 4 (a) and 4 (b) are graphs showing micro-bubble removal and sound pressure fluctuation in general water in one embodiment of the present invention. Fig.
Figure 5 is a schematic diagram illustrating sound pressure measurements in a sample holder filled with water in an ultrasonic device in one embodiment of the present invention;
6 (a) to 6 (d) are graphs showing the results of measurement of a solvent (Fig. 6 (a) and (b)) in which microbubbles are not removed (C) and (d) of Fig.
7 is a graph showing the zeta potential of a 2D material ultrasonically treated in a solvent (blue) in which fine bubbled solvent (red) and fine bubbles exist, in one embodiment of the present invention.
FIG. 8 is a graph showing the pH measurement of five 2D materials after ultrasonic treatment, with and without removal of solvent microbubbles, according to one embodiment of the present invention.
Figures 9 (a) - (d) show XPS data of water-sonicated flakes and powders of MoS ₂ , and water-ultrasonic treated flakes and powders of h- BN, in one embodiment of the invention.
10 (a) to 10 (e) are graphs showing the TEM image (upper row) and the thickness distribution of the stripped flakes (lower row), respectively, in one embodiment of the present invention.
11 is an image showing a printed pattern using nozzle inkjet printing using a graphene ink on a PET substrate in one embodiment of the present invention.
12A is an image of a 2D material solution dispersed in deionized water for one week in one embodiment of the present invention.
12B is a graph showing the stability of graphene, h- BN, and MoS ₂ stored at high temperature (60 ° C) after ultrasonication according to the presence or absence of microbubbles in one embodiment of the present invention.
12C is a graph showing the stability of graphene, h- BN, and MoS ₂ stored at high temperature (60 ° C) and low temperature (20 ° C) after ultrasonic treatment after microbubbles removal in one embodiment of the present invention.
13 (a) and 13 (b) show the XPS spectrum of graphene ultrasonically treated in the case of a solvent in which microbubbles were not removed and in a solvent in which microbubbles were removed, in one embodiment of the present invention, and Fig. 13 (C) and (d) show the Raman spectra of graphene flakes and graphite powder water-stripped in the central region in one embodiment of the invention.
14 (a) to 14 (c) are low-resolution TEM images of flakes of graphene, h- BN and MoS ₂ , respectively, in one embodiment of the present application, , An enlarged TEM image showing the crystal structure of graphene, h- BN, and MoS ₂ , respectively, in one embodiment of the present application.
Figs. 15A to 15C are images showing characters, lines, and mesh patterns printed using graphene, h- BN, and MoS ₂ ink, respectively, in one embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. It should be understood, however, that the present invention may be embodied in many different forms and is not limited to the embodiments described herein. In the drawings, the same reference numbers are used throughout the specification to refer to the same or like parts.

Throughout this specification, when a part is referred to as being "connected" to another part, it is not limited to a case where it is "directly connected" but also includes the case where it is "electrically connected" do.

Throughout this specification, when a member is " on " another member, it includes not only when the member is in contact with the other member, but also when there is another member between the two members.

Throughout this specification, when an element is referred to as " including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise. The terms " about ", " substantially ", etc. used to the extent that they are used throughout the specification are intended to be taken to mean the approximation of the manufacturing and material tolerances inherent in the stated sense, Accurate or absolute numbers are used to help prevent unauthorized exploitation by unauthorized intruders of the referenced disclosure. The word " step (or step) " or " step " used to the extent that it is used throughout the specification does not mean " step for.

Throughout this specification, the term " combination (s) thereof " included in the expression of the machine form means a mixture or combination of one or more elements selected from the group consisting of the constituents described in the expression of the form of a marker, Quot; means at least one selected from the group consisting of the above-mentioned elements.

Throughout this specification, the description of "A and / or B" means "A or B, or A and B".

Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to these embodiments and examples and drawings.

A first aspect of the present invention provides a method of producing a two-dimensional material dispersion, comprising adding a two-dimensional material to a solvent from which microbubbles have been removed and then separating and dispersing the two-dimensional material by ultrasonic treatment.

In an embodiment of the present invention, the solvent from which the microbubbles are removed may be, but not limited to, a microbubble eliminator in which a solvent is put into operation to remove microbubbles.

In one embodiment of the invention, the two-dimensional material is graphene, boron nitride (h-BN), a metal radical chalcogenides, BSCCO (bismuth strontium calcium copper oxide), CdTe, GaS, GaSe, GaS _{1 - x} Se _{x , CdI 2, PbI 2, K} 2 Al 4 (Si 6 Al 2 O 28) (OH, F) 4, or _{Mg 6 (Si 8 O 28)} (OH) may be to include _four, but not limited to, . The two-dimensional material may be, but is not limited to, being added to a solvent from which microbubbles have been removed, and then peeled off as a monolayer material from the multi-layer material by ultrasonic treatment.

In one embodiment of the invention, the metal dicalcogenide is selected from the group consisting of molybdenum disulfide (MoS ₂ ), molybdenum diselenide (MoSe ₂ ), molybdenum diterlide (MoTe ₂ ), tungsten disulfide (WS ₂ ), tungsten dicerenide (WSe ₂ ), tungsten ditelluride (WTe ₂ ), niobium disulfide (NbS ₂ ), niobium diselenide (NbSe ₂ ), niobium ditelluride (NbTe ₂ ), tantalum disulfide (TaS ₂ ) (TaSe ₂ ), tantalum ditelylide (TaTe ₂ ), hafnium disulfide (HfS ₂ ), hafnium decelenide (HfSe ₂ ), hafnium ditelluride (HfTe ₂ ), titanium disulfide (TiS ₂ ) (TiSe ₂ ), or titanium ditelylide (TiTe ₂ ).

In one embodiment of the present invention, the graphene can be separated from a two-dimensional material that does not disperse in water in which fine bubbles exist, or water that has been removed from fine bubbles, or can be dispersed in water when stored at a high temperature for a long period of time have.

In one embodiment of the present invention, the graphene may be easily dispersed in the solvent in which the microbubbles are removed by functionalization of the edge by a hydroxyl group or a carboxyl group, but may not be limited thereto.

In one embodiment of the present invention, the solvent may be, but not limited to, water, an alcohol, or an organic solvent. For example, the alcohol may include, but is not limited to, methanol, ethanol, or propanol. The organic solvent may include an aliphatic or aromatic organic solvent and may include, for example, dimethylformamide (DMF), dimethylacetamide (DMA), dimethylsulfoxide (DMSO), methylene chloride methylenechloride (MC), chloroform, CCl ₄ , propyleneglycol methyl ether acetate (PGMEA), or N-methylpyrrolidinone (NMP) .

In one embodiment of the present invention, the ultrasonic sound pressure in the solvent from which the microbubbles are removed may be about 1 kPa or more, but the present invention is not limited thereto. For example, the sonic pressure of the sonication may be at least about 1 kPa, at least about 5 kPa, at least about 10 kPa, at least about 20 kPa, at least about 30 kPa, at least about 40 kPa, at least about 50 kPa, At least about 150 kPa, at least about 200 kPa, at least about 250 kPa, at least about 300 kPa, at least about 350 kPa, at least about 400 kPa, from about 1 kPa to about 400 kPa, from about 1 kPa to about 350 kPa, From about 10 kPa to about 250 kPa, from about 10 kPa to about 400 kPa, from about 10 kPa to about 350 kPa, from about 10 kPa to about 300 kPa, from about 10 kPa to about 250 kPa, from about 20 kPa to about 400 kPa, from about 20 kPa to about 300 kPa, from about 20 kPa to about 300 kPa, from about 20 kPa to about 250 kPa, from about 30 kPa to about 400 kPa, from about 30 kPa to about 350 kPa, from about 30 kPa to about 300 kPa, But is not limited to, from about 30 kPa to about 250 kPa, from about 40 kPa to about 400 kPa, from about 40 kPa to about 350 kPa, from about 40 kPa to about 300 kPa, or from about 40 kPa to about 250 kPa .

In one embodiment of the present invention, the higher the temperature of the solvent, the better the dispersion stability of the two-dimensional material may be, but the present invention is not limited thereto.

In one embodiment of the invention, the two-dimensional material dispersion may be one that does not contain a compound or a surfactant, but may not be limited thereto.

A second aspect of the invention provides an ink comprising a two-dimensional material dispersion prepared according to the method of the first aspect of the present application. Although the detailed description of the parts overlapping with the first aspect of the present application is omitted, the description of the first aspect of the present invention can be applied equally to the second aspect.

In one embodiment of the present invention, in the two-dimensional dispersion experiment, ultrasonic treatment in a solvent in which microbubbles are removed may be advantageous for synthesizing a two-dimensional material having good dispersion stability in water. The use of pure water to strip and disperse 2D materials can also be of benefit in the research required in economical industrial or commercial applications and water-based experiments. To date, ultrasonic cavitation can only be used for physical exfoliation of two-dimensional materials through the braking of thinner platelets of bulk stratified materials. However, in one embodiment of the invention, an initial synthesis of water-soluble graphene by ultrasonic reaction through ultrasound in a solvent in which microbubbles have been removed is presented. In one embodiment herein, the two-dimensional material dispersion can contribute to the development of large capacity and economical synthesis methods for two-dimensional materials using ultrasonic chemistry. The inkjet printing description using water-dispersed two-dimensional-material inks suggests a great potential for practical applications.

Graphene and other two-dimensional materials are known to not readily dissolve in water without the use of other compounds or surfactants.

However, in one embodiment of the present invention, the two-dimensional material dispersion is readily prepared by stripping or dispersing such materials in the solvent by simply removing the microbubbles present in the solvent (e.g., water) A method can be suggested. For example, due to the extreme high temperature and pressure locally induced by ultrasonic cavitation when sonicating in the solvent from which the microbubbles have been removed, the graphene is edge-functionalized at the edge, And can be stably dissolved in water for more than one month. However, graphene sonicated in water in the presence of microbubbles may not be stably dispersed in water due to the reduced sonochemical reaction. In addition, two-dimensional materials such as h-BN, MoS ₂ , WS ₂ , and MoSe ₂ in the solvent from which the microbubbles have been removed can be well dispersed even at low temperatures. This stable dispersion appears to be due to the formation of an electric double layer resulting from a relatively high dielectric constant. Additionally, elevated storage temperatures (60 ° C or higher) can improve long term dispersion stability compared to lower storage temperatures (20 ° C). Accordingly, the two-dimensional material dispersion according to one embodiment of the present invention can be easily applied as ink in inkjet printing.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto.

[ Example ]

<Materials and Apparatus for Sample Preparation>

For sample preparation, graphite and MoSe ₂ powder were purchased from Alfa Aesar. Hexavalent boron nitride (h-BN) powder was purchased from Momentive. MoS ₂ and WS ₂ were purchased from Sigma Aldrich.

To remove and disperse the two-dimensional (2D) material in water from the source powder, water was first added to the FiberFlo Polyproptlene Degas Nodule (MINNTECH) apparatus to remove microbubbles in the water. Subsequently, each material (20 mg) was sonicated in water (200 mL) in which the microbubbles were removed for 60 hours by a bath sonicator manufactured by Onejon Ultrasonic. The operating power was 20 W and the frequency was 40 kHz. The resulting solution was centrifuged at 600 RCF for 30 minutes using a high speed centrifuge (Supra 25K, HANIL SCIENCE INDUSTRIAL). The centrifuged final solution was maintained at atmospheric conditions (20 DEG C) or in an oven (60 DEG C).

<Measurement of dispersion stability>

After the centrifugation process, the dispersion stability was measured using a UV-VIS-NIR spectrophotometer to confirm how stable the flakes were dispersed in the microbubbles-free water. After the centrifugation, the obtained solution was put into a standard 1-cm path quartz cell and the absorbance was measured at intervals of 3 days for one month. Stability was indicated by absorbance at 650 nm, normalized by the first measured value. Absorbance at 650 nm is generally used to compare the stability of graphene in dispersion studies. The stability of MoS ₂ and WS ₂ in water with microbubbles removed is shown in FIG. The WS ₂ stored at high temperature was fairly stable in water for a month while the stability at low temperature was slightly lower. It can be seen that the stability of WS ₂ dispersed in microbubbles-free water, such as graphene, h-BN and MoS ₂ dispersions, depends on the storage temperature. However, the solubility of MoS ₂ dispersed in the water from which the microbubbles were removed was high in both high temperature and low temperature storage. It is noteworthy that once MoSe ₂ is stripped in water, the dispersion of MoSe ₂ can be very stable regardless of the storage temperature.

< FT - IR  Analysis>

Measurements of FT-IR spectroscopy were performed and it was determined whether graphene was functionalized during ultrasonication in microbubbles free water. A graphene film was prepared on a quartz substrate by using a filter tool. For the preparation of the graphene film, the centrifuged dispersion of graphene was filtered using a 0.02 μm pore 13 φ anodisc, and the graphene film on the membrane was applied to the surface of the NaOH solution (1 M) for 3 hours And the anodisc membrane was dissolved. After the membrane was removed, the dispersed graphene film was carefully transferred onto the quartz substrate. The film was dried at 160 &lt; 0 &gt; C under argon flow. As soon as the drying process was terminated, FT-IR spectroscopic analysis of the film was performed using IFS 66 v / s provided by Bruker optics. Figure 2 shows FT-IR data of graphene, h-BN, and MoS ₂ . All spectra showed two SiO ₂ peaks near 1000 cm ^-1 (Si-O-Si stretching) and 800 cm ^-1 (Si-O bending). Generally, OH stretching vibration region is 2,900 cm ^-1 and 3,700 cm ^{- 1.} As shown in Fig. 2, the present example was able to confirm a broad and strong peak at 3,000 cm ^-1 to 3,650 cm ^-1 . The peak is the clearest evidence of the presence of hydroxyl groups. The signal was not found in the starting graphite powder. The results suggest that graphene was functionalized during sonication. However, there was no evidence of OH stretching in other materials. In the h-BN spectrum, a peak was found at 1,370 cm ^-1 . As shown in the h-BN spectrum, one peak was observed at 1,370 cm ^-1 , but the band exhibited plane ring vibration (E1u mode).

<Raman spectroscopic analysis>

Raman spectroscopic analysis was performed and the quality of the nanosheets of h-BN, MoS ₂ , WS ₂ , and MoSe ₂ peeled off in water was confirmed. A film was prepared on a silicon oxide substrate for measurement. The preparation was identical to that of the graphene film for FT-IR spectroscopy, except for the base material. The excitation wavelength was 532 nm. Figure 3 (a) shows typical peaks of h-BN flakes. As shown in Fig. 3 (e), the peak position was almost the same as that of the h-BN powder used as the raw material. It is noted that this tendency may also occur in other materials. From the Raman spectra of the four materials, no oxide peak could be found, indicating that it was not oxidized during synthesis (FIG. 3).

<Principles of sonic cavitation>

It was found that the sound pressure level of the ultrasonic treatment in the solvent in which the microbubbles were removed was much higher than that of the solvent in which the microbubbles were present. This implies that the sonic wave generated from the sonic vibrator is much more absorbed with ultrasonic treatment in the solvent in which the microbubbles are present. That is, the sound pressure amplitude P _A decreases because the sound wave velocity is easily absorbed into the minute bubbles. Therefore, it is required to confirm the sound pressure according to the minute bubble removal time. In addition, the above-mentioned P _A is an important parameter for cavitation in water during the ultrasonic treatment process, and is one of the important factors for peeling and functionalization of graphene. Generally, larger sound pressure can generate more air bubbles. However, the bubbles collapse to peel off the layered material and to functionalize the edge of the graphene nanosheet. According to the ultrasonic chemical theory, when the negative pressure exceeds the internal pressure of the bubble, the bubble is destroyed. The following equation 1 describes the relationship between P _A and P _g .

P _g = P ₀ + P _A cos? T + 2? / R _c (Equation 1)

The P _g , P ₀ , P _A , δ and R _c indicate the water vapor pressure, the amplitude of sound pressure, the atmospheric pressure, the average surface tension of water, and the critical radius of the bubbles (FIG. Since the above 2? / R _c is very small, the above condition can be ignored in the present embodiment. Table 1 below shows P _g , P _A , and P ₀ in the presence of microbubbles and upon removal of microbubbles.

[Table 1]

As shown in Fig. 4 (a), it was found that the negative pressure measured in the solvent from which the microbubbles were removed exceeded the difference between the atmospheric pressure and the vapor pressure. The bubble can be broken at this temperature. However, FIG. 4 (b) shows that when the microbubbles are present, the negative pressure can not reach the vapor pressure. It is not easy for bubbles to collapse when fine bubbles are present. Thus, it was concluded that the solvent from which the microbubbles had been removed resulted in a sound pressure sufficiently high for peeling and functionalization of the edge of the graphene sheet.

<Measurement of sound pressure>

As shown in Fig. 5, the beakers were placed in three positions in a bass sonicator, and the position-dependent change of the sound pressure was confirmed. To prevent contamination of the probe and workpiece from the particles, each beaker was filled with deionized water free of particles. The sound waves were measured at the center of the beaker at 5 ms using a hydrophone (Gearing & Watson D / 140) to obtain sound pressure data.

Figure 6 shows transient waveforms and spectra at two different conditions of the sonication bath. 6 (a) shows a temporal waveform in the presence of minute bubbles, Fig. 6 (b) shows a frequency spectrum in the presence of minute bubbles, Fig. 6 (c) ) Shows the frequency spectrum after microbubbles removal. The major frequency peak appeared around 37 kHz. The frequency peak may vary depending on the presence of fine bubbles in the solvent and the dissolved particles. The measured sound pressures and average sound pressures at three different positions for the two conditions are shown in Table 2 below and there was no significant change in position.

[Table 2]

<2D in water Flake Electrochemical Potential >

The zeta potential of the centrifuged dispersion was measured using a zetasizer (NANO ZS, Malvern instruments). Generally, when the zeta potential is lower than -30 mV, the amount of flakes dispersed in water is considerably superior. Ultrasonic treated graphene in the microbubbles-free solvent was lower than -30 mV. Considering only the zeta potential value, the graphene synthesized by this example was much better than the reduced graphene oxide (Fig. 7). However, graphene produced at low temperatures had a poor zeta potential. Other materials had a stable zeta potential in water, regardless of the sonication conditions.

< pH  Measurement>

The state of the solution was confirmed by measuring the hydrogen index of the aqueous solution using a pH meter (E-sweep, Seiko Instruments Inc.). Figure 8 shows the pH values of all materials dispersed in water.

< XPS  Measurement>

XPS analysis was performed to investigate the functional groups of graphene, h-BN, and MoS ₂ flakes peeled off from the microbubbles-free solvent. Each dispersion of graphene, h-BN, and MoS ₂ was dropped using a pipette until the flakes completely covered the substrate on the quartz substrate. The thin film on the quartz substrate was annealed at 160 캜 under an argon gas flow. This example analyzed samples using a K-Alpha X-ray photoelectron spectrometer system and a monochromated Al x-ray source. The assay scan was -50 eV and the step size was 0.1 eV. A flood gun was used for charge compensation.

9 (a) and 9 (b) show XPS data of MoS ₂ powder, and MoS ₂ flakes were respectively synthesized by this embodiment. Due to the S binding to Mo showed several peaks indicating the MoS _2, such as relating 3d _3/2 and 3d _5/2 peak and Mo, and S 2s peak. There is also a MoO ₃ peak, which means the oxide bound to Mo. There was little difference between MoS ₂ flake and MoS ₂ powder. MoO ₃ peaks was observed in the two spectra, at.% And the proportion of MoS ₂ flakes was noted that similar to that of MoS ₂ powder. From the MoO ₃ peak and atomic% of O, this example showed that MoS ₂ flakes in water were functionalized opposite to graphene in water. In addition, as shown in Figs. 9 (c) and 9 (d), the h-BN flakes were not functionalized during ultrasonic treatment.

&Lt; Sheet thickness Low resolution TEM  Images and distribution>

The nanosheets were further analyzed using TEM. For the measurement, a drop of the dispersion was cast on a holy carbon grid (400 mesh) during the measurement. The low-resolution TEM image was performed using an FE-TEM manufactured by JEOL Ltd. with an acceleration voltage of 2,000 kV. Figure 10 shows a typical image of a 2D material. This embodiment can observe a single layer, folded single layer or double layer, and multiple layers. Also, as shown in Fig. 10, the thickness distribution of the sheet was plotted through investigation in the TEM results. The graphene monolayer appeared to be about 10%, and about 87% of the observed flakes were less than four layers. It was found in this example that the monolayer of materials other than graphene was also about 10%, and even the monolayer of MoS ₂ was observed at about 20%. In practice, it was found that the dispersion prepared in this example contains very thin nanosheets.

< Inkjet  Printing method>

In this example, 4 parts by weight of poly (ethylene oxide) (PEO) powder (average Mw ~ 1,000,000, Sigma Aldrich) were dissolved in a mixed solvent of 60 parts by weight deionized water (DI water) and 40 parts by weight ethanol. To prepare a viscoelastic homogeneous ink, a solution of PEO in the water / ethanol mixture was added to the graphene, MoS ₂ , and h-BN dispersions in appropriate proportions using a THINKY mixing machine (Thinky Inc, ARE-310) .

In this embodiment, an EHD printer (Enjet Inc, Korea) was used. Micro-syringe pumps were used to supply 2D materials (graphene, MoS ₂ , and h-BN) / PEO synthetic dispersions from a 1 mL syringe into metal nozzles. The nozzle was a 32 G (ID: ~ 0.23 mm, OD: ~ 0.10 mm) stainless steel needle. The distance between the tip and the collector was adjusted around 2.5 mm to stabilize the near-zone fiber jet, ensuring an ohmic flow region. For EHD printing on Si and SiO ₂ substrates, a high voltage of about 1.8 kV to about 2.2 kV was applied on a metal transfer stage. Although the Si / SiO ₂ substrate has an insulating surface, the ink can be successfully printed by the EHD jet printer because the insulating layer maintains a high electric field between the nozzle tip and the grounded stage It is thin enough. In order to make a pattern on a PET substrate, an electric field may not be applied. Thus, the ink was simply released by syringe pressure. This method is called nozzle inkjet printing. The printed mesh pattern is shown in Fig.

To separate and disperse the 2D material in water, this example adjusted the amount of microbubbles. This example tested several 2D materials for underwater stripping, namely graphene, h-BN, MoS ₂ , WS ₂ , and MoSe ₂ , and observed that high temperatures are generally beneficial for stripping and dispersion stability. However, depending on the material, the dispersion mechanism was different due to the surface characteristics. This example synthesized an atomic layer platelet in water using a bulk stratified material powder. They were added to deionized water and sonicated in a bath sonicator for about 60 hours. In order to remove minute bubbles, a solvent to be used in the microbubbles removing device was added and microbubbles were removed. After sonication, the solution of the detached 2D material was centrifuged at 600 RCF (relative centrifugal force) and separated into thin pieces. The dispersed thin 2D material in water was stored for about one month at both high temperature (60 占 폚) and low temperature (20 占 폚) to observe the temperature dependence of long term stability. For the synthesis and storage experiments, this example uses high temperature (60 &lt; 0 &gt; C) and low temperature (20 &lt; 0 &gt; C) for long term solution stability of the material and a solvent in which fine bubbles are removed, did.

12A shows a 2D material dispersed in water, and the dispersion was peeled off in a solvent (water) from which fine bubbles were removed and stored at a high temperature (60 DEG C). The nanoparticles were stably dispersed for more than one month. In the microbubbles-free water, the color of each material was black for graphene, mauve-white for h-BN, dark-yellow for MoSe ₂ , yellow for WS ₂ , and light-brown for MoSe ₂ . All tested materials were stably dispersed by the solvent in which the microbubbles were removed and then stored. The long-term stability of the dispersion of the 2D material in the microbubbles free water was investigated by measuring the absorption ratio with time using a UV-vis spectrophotometer. 12B and 12C, squares, circles, and triangles in the graph represent graphene, h-BN, and MoS ₂ , respectively. As shown in FIG. 12B, the stability results suggested that the material was stably peeled off and stored at high temperature (60 ° C) for one month in the solvent from which microbubbles were removed. On day 10, most of these materials were stable without further sedimentation. Graphene showed the highest stability with 90% dispersion even after one month. The stability was not quantified after more than one month, but this example observed that the color of the graphene solution did not change significantly after one year. The high stability of the graphene is presumably due to optimization of the synthesis process for graphene at an early stage.

Thus, if the process is applied to other materials, their solution stability may be improved. Most of the exfoliated material in the solvent in which fine bubbles exist is well dispersed. However, only graphene flake generated precipitates rapidly for 3 days, indicating that the solvent-sonicated graphene in which microbubbles were present was unstable in water. To investigate the dependence of dispersion stability at the storage temperature, the peeled material was stored at 60 ° C or 20 ° C in the solvent from which the microbubbles were removed. As shown in FIG. 12C (and WS ₂ and MoSe ₂ in FIG. 1), the material stored at a generally high temperature was more stable than the material stored at a low temperature. According to colloid theory, colloids or molecules are well dispersed at higher temperatures because of the higher kinetic energy of the molecules and the vigorous Brownian motion, which prevents flocculation and precipitation. The results of the theoretical work also suggest that liquid molecules located between the 2D material sheets will exhibit high energy barriers to effectively disperse the 2D material. Although stability may seem to decrease for a long time in the case of low temperature storage, this example observed that the precipitation completely disappeared after about 40 days and observed that the solution maintained the same color for more than one year. The stripping and solution stability experimental results show that after the 2D material was synthesized at high temperature by ultrasonication in water, the solution was fairly stable at temperatures above room temperature.

Two questions arise from the temperature dependence of the synthesis. First, graphene synthesized in a solvent in which microbubbles have been removed is stable in water, whereas graphene produced in a solvent in which microbubbles are present is unlike other 2D materials. The second was how the other materials were stably dispersed in water even at lower ultrasound and storage temperatures. In connection with the first question, previous experience with graphene dispersion provided insights. Graphene is not readily soluble in water, but graphene oxide is well dispersed, which is due to surface functional groups. However, in the solvent in which the microbubbles are removed, the graphene peeled off is functionalized, whereas the graphene ultrasonically treated in the solvent in which the microbubbles are not removed is not functionalized. To investigate the functionalization of graphene after ultrasonic treatment, a spectral analysis fingerprint of the edge functionalization of graphene was shown in Figures 13 (a) to 13 (d). 13 (a) and 13 (b), this example uses a X-ray photoelectron spectroscopy (XPS) method to measure the amount of the fine bubbles in the solvent from which the fine bubbles have not been removed, Respectively. XPS spectra of graphene synthesized by ultrasonic treatment in a solvent in which microbubbles were removed showed functional group vaporization of graphene having a carboxyl group and a hydroxy group while the spectrum of graphene prepared by ultrasonication in a solvent in which microbubbles were not removed Showed negligible amounts of the functional groups.

To demonstrate the functionalization of graphene samples, FT-IR spectroscopy was performed and the results also confirmed functionalization (Figure 2). To confirm that these functional groups are attached to the surface, such as at graphen oxide or at the edge, this example performed Raman spectroscopy on a single graphene flake from the ultrasonic treatment in the solvent in which the microbubbles were removed . The Raman spectra collected from the central region showed a negligible D-peak, indicating the functionalization or defect of graphene (Fig. 13 (c)). The Raman spectrum of bulk graphite, a raw material of graphene synthesis, showed a similar peak shape except for the D-peak from the edge of the layer (Fig. 13 (d)). Spectroscopic analysis showed that the ultrasound treated graphene was only functionalized at its edge and the functional group improved the solubility of graphene in water. These results can raise another question as to how graphene is functionalized when ultrasonicated in a solvent in which microbubbles are removed. In an ultrasonic treatment bath, cavitation occurred due to sudden pressure fluctuations. The cavitation was bubbling in water and disintegration within milliseconds. The foam collapse induced a fairly high local temperature of about 5,000 DEG C and a high local pressure of 10,000 bar. Because at these high temperatures and pressures water can be decomposed into chemically volatile H ⁺ and OH ^- , cavitation provides sufficient energy and can break chemical bulk reactions and cause chemical reactions with water. This type of ultrasonic chemical reaction (ultrasound) has been studied for the synthesis of various nanomaterials [KS Suslick, Sonochemistry. Science 247, 1439-1445 (1990). Because it has dangling carbon atoms, it reacted more readily with radicals or ions than in the graphene in-plane region. In cavitation by ultrasonic agitation, the sound pressure amplitude was much greater at that temperature than the difference in atmospheric pressure and boiling pressure. The difference was about 1 atm under ambient conditions. As sound propagated in matter, pressure was reduced by energy absorption. In water, the reduction level was smaller for the solvent from which the microbubbles were removed, which meant that the sonic pressure was higher than in the solvent from which the microbubbles were removed. This example measures the sound pressure in a bass for two different conditions (Figures 5 and 6). In solvents with microbubbles removed, the sound pressure varied by 2.3 atm, which was easily induced by cavitation, while that in microbubbles-free solvents varied by 0.4 atm. However, in the solvent from which the microbubbles have been removed, the pressure fluctuation level can induce cavitation violently, while not in the solvent in which the microbubbles are not removed. With respect to the second question raised above, another factor must be that there are other factors to induce the degradation of the 2D material in water, regardless of the synthesis conditions. Unlike graphene, the dispersion of h-BN, MoS ₂ , WS ₂ , and MoSe ₂ remains stable when dispersed through microbubbles removal and, if not, by ultrasonic treatment, which results in the removal of microbubbles from solvent- As in the case of graphene treated, edge functionalization was not the cause of the high water solubility of these materials. Since the materials are less electrically conductive than graphene, electrical double layers can be formed on their surfaces and these materials could be easily dispersed in water without aggregation or precipitation. This point can be supported by zeta-potential measurements because the stability of the nanoparticle solution is closely related to the electrical double layer on the surface of the nanoparticle. Generally, a dispersed material having a zeta-potential value of about 30 mV or less is stable in a solvent. As shown in FIG. 7, the zeta-potential values of the h-BN, MoS ₂ , WS ₂ , and MoSe ₂ dispersed samples were all about -30 mV regardless of the ultrasonic treatment conditions. The zeta-potential of solvent-ultrasonically treated graphene with microbubbles removed showed a positive sign in this regard. However, the zeta-potential of the ultrasonically treated graphene sample in the solvent in which the microbubbles were not removed was -13 mV, and the sample showed low solution stability. Thus, the zeta-potential results supported our discussion of microbubble-dependent dispersion mechanisms in water.

The pH of the dispersion solution may vary during the ultrasonic treatment due to the ultrasonic reaction, and this change may affect the solubility. In the case of graphene and h-BN, the pH is not nearly the same. Thus, the pH appears to have no effect on the solubility of graphene and h-BN. However, the MoS ₂ and WS ₂ solutions were acidified after ultrasonication. To investigate the effect of pH on solubility, this example measured the pH of the aqueous solution of the raw material powder and observed that it was similar to the pH value of the dispersed 2D material solution. However, the particles in the powder solution precipitated irrespective of the micropore, in contrast to the ultrasonic treated solution. These results indicated that the pH was not a major contributor to the high solubility of the 2D material (Figure 8).

To investigate the amount of flaked flakes, this example collected a high-resolution transmission electron microscope (TEM) image, as shown in Figures 14 (a) - (f). The crystal structure of the material was well aligned without defects. The image showed some damage or chemical reaction on the surface of the material during ultrasonic treatment. At the graphene edge, the atom was not recognized, which was an indirect indication of the edge functionalization of graphene. In contrast, the edge atoms of h-BN were well aligned without signaling of functionalization. From previous reports on water dispersion of h-BN, it can be assumed that the excellent dispersion of h-BN is due to the edge functionalization despite the hydrophobic surface. However, the TEM observation of this example showed that h-BN was not well dispersed due to functionalization. In addition, previous theoretical studies have provided evidence that the oxides are hardly oxidized due to thermodynamic instability. The TEM image of MoSe ₂ also showed that the crystal structure was not damaged or oxidized at least at its center from the ultrasonic treatment. The XPS results of h-BN and MoS ₂ (FIG. 9) were confirmed not to be oxidized across the entire surface, including the edges, as shown by the absence of a change in energy peak after ultrasonic treatment. As shown in FIG. 10, this example determined the thickness distribution of the dispersed flakes using low resolution TEM images. The second to third layers were most frequently observed in dispersed materials. The size of the flakes was from about 200 nm to about 300 nm.

The water-based synthesis method is easy, economical and the materials are well dispersed. In addition, various applications may be possible. As described, this embodiment performed inkjet printing using a dispersed 2D-material solution. As shown in FIG. 15, this example attempted electrohydrodynamic (EHD) printing on Si / SiO ₂ and applied some electric field between the nozzle and substrate to form graphene, h-BN, and MoS ₂ To print letters, lines, and mesh patterns. In this embodiment, a mesh pattern was formed on a plastic substrate (PET) using a nozzle printing method using graphene ink, and no electric field was applied (FIG. 11). Since the printed material has good electrical properties as a conductor (graphene), an insulator (h-BN), and a semiconductor (MoS ₂ ), the ink could be applied to printed electronic devices. In the test, this embodiment was able to easily print lines and characters having a width of 20 mu m in a normal printer manner. Line width was limited by nozzle size, and narrower lines could be printed using smaller printer nozzles. The printing results indicated that the ink had essentially no impairment that interfered with its actual use.

It will be understood by those of ordinary skill in the art that the foregoing description of the embodiments is for illustrative purposes and that those skilled in the art can easily modify the invention without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims (7)

Removing the two-dimensional material by ultrasonic treatment after adding the two-dimensional material to the solvent from which the fine bubbles have been removed,
A method for producing a two-dimensional material dispersion.
The method according to claim 1,
The two-dimensional material is graphene, boron nitride (h-BN), a metal radical chalcogenides, BSCCO (bismuth strontium calcium copper oxide), CdTe, GaS, GaSe, GaS _{1 - x} Se _x, CdI _2, PbI _2, K ₂ Al ₄ (Si ₆ Al ₂ O ₂₈ ) (OH, F) ₄ , or Mg ₆ (Si ₈ O ₂₈ ) (OH) ₄ .
3. The method of claim 2,
The metal radical chalcogenides are molybdenum disulfide (MoS _2), molybdenum di selenium arsenide (MoSe _2), molybdenum di telru fluoride (MoTe _2), tungsten disulfide (WS _2), tungsten di selenium arsenide (WSe _2), tungsten di telru fluoride (WTe _2), niobium disulfide (NbS _2), niobium di selenium arsenide (NbSe _2), niobium di telru fluoride (NbTe _2), tantalum disulfide (TaS _2), tantalum di selenium arsenide (TaSe _2), tantalum di telru fluoride (TaTe _2), hafnium disulfide (HfS _2), hafnium di selenium arsenide (HfSe _2), hafnium di telluride (HfTe _2), titanium disulfide (TiS _2), titanium di-selenium arsenide (TiSe _2), or titanium di Lt; RTI ID = 0.0 &gt; (TiTe2). &Lt; / _RTI &gt;
The method according to claim 1,
Wherein the solvent comprises water, an alcohol, or an organic solvent.
The method according to claim 1,
Wherein the ultrasonic sound pressure in the solvent from which the microbubbles are removed is 1 kPa or more.
The method according to claim 1,
Wherein the two-dimensional material dispersion does not contain a compound or a surfactant.
6. An ink, comprising a two-dimensional material dispersion prepared according to the method of any one of claims 1 to 6.

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