WO2015102191A1 - Method for preparing molybdenum disulphide nanosheet, stripping liquid therefor and molybdenum disulphide nanosheet prepared thereby - Google Patents

Abstract

Provided is a method for preparing a molybdenum disulphide (MoS2) nanosheet comprising the steps of: mixing bulk MoS2 powder with an organic solvent containing a stripping accelerant comprising an alkali metal or an alkaline earth metal and a hydroxyl radical; and preparing an MoS2 nanosheet by sonicating the mixed bulk MoS2 powder.

Description

Method for preparing molybdenum disulfide nanosheets, stripping solution therefor and molybdenum disulfide nanosheets prepared thereby

The present invention relates to a method for preparing molybdenum disulfide nanosheets, a stripping solution for the same, and a molybdenum disulfide nanosheet prepared thereby, and more specifically, to increase the yield of molybdenum disulfide (MoS2) nanosheets and to reduce the sonication time and economical efficiency. An improved method for producing molybdenum disulfide nanosheets, a stripping solution therefor, and molybdenum disulfide nanosheets produced thereby.

2D layered nanomaterials are of great interest for new approaches to low-dimensional systems. Transition metal dichalcogenides (MX ₂ (M = Mo, W; X = S, Se, Te)) belong to a family of layered structures, in which covalent XMX monolayers, like graphite, are joined by van der Waals forces Are piled up.

Each single layer consists of two chalcogen (X) atomic layers and a metal atom layer, which are inserted into two layers of chalcogens. Prior art (B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti and A. Kis, Nat. Nanotechnol., 2011, 6 , 147., KF Mak, C. Lee, J. Hone, J. Shan and TF Heinz, Phys. Rev. Lett., 2010, 105 , 136805, KK Kam and BA Parkinson, J. Phys. Chem., 1982, 86 , 463.), MX ₂ has a band gap of 1.1 eV to 2.0 eV. Proved that there is. In the case of molybdenum disulfide (MoS ₂ ), there is a transition from an indirect band gap (1.2 eV) to a direct band gap (1.8 eV) in a single layer in the bulk, and thus, in energy storage, catalysis, sensors and electronics. Applicability to various fields is being studied.

However, since MoS ₂ is not only an insoluble compound but also nonvolatile, it is known that it is very difficult to prepare a thin film. Mechanical methods using Scotch-tape were used for the extraction of a stable monolayer of MX ₂ . In addition, a technique for peeling three-dimensional structures into two-dimensional nanosheets in a liquid phase was also introduced, which is one of the most efficient methods for mass production of MX ₂ nanosheets (JN Coleman, M. Lotya). , A. O'Neill, SD Bergin, PJ King, U. Khan, K. Young, A. Gaucher, S. De, RJ Smith, IV Shvets, SK Arora, G. Stanton, H.-Y. Kim, K Lee, GT Kim, GS Duesberg, T. Hallam, JJ Boland, JJ Wang, JF Donegan, JC Grunlan, G. Moriarty, A. Shmeliov, RJ Nicholls, JM Perkins, EM Grieveson, K. Theuwissen, DW McComb, PD. Nellist and V. Nicolosi, Science, 2011, 331, 568.HSSR Matte, A. Gomathi, AK Manna, DJ Late, R. Datta, SK Pati and CNR Rao, Angew.Chem.Int.Ed., 2010, 49, 4059.G. Eda, H. Yamaguchi, D. Voiry, T. Fujita, M. Chen and M. Chhowalla, Nano.Lett ., 2011, 11, 5111).

Li-intercalation in the MoS2 stripping technique is a useful method for stripping. However, this method has a problem in that process control is difficult because it is very sensitive to ambient environmental conditions. In addition, due to lithium intercalation (Li-intercalation) there is a problem that the original MoS ₂ phase transition occurs. Recently, a technique for producing a MoS ₂ dispersion having a thickness of 3-12 nm by peeling directly from an organic solvent through ultrasonication has been disclosed. Hijaman, this method also shows a low yield and there is a problem that long sonication time is required to improve the concentration.

Therefore, the problem to be solved by the present invention is to increase the yield of molybdenum disulfide (MoS2) nanosheets, and to improve the economic efficiency by reducing the ultrasonic treatment time, and the method for producing molybdenum disulfide (MoS2) nanosheets, and the peeling liquid and thereby used To provide a molybdenum disulfide (MoS2) nanosheets prepared.

In order to solve the above problems, the present invention comprises the steps of incorporating a bulk molybdenum disulfide (MoS2) powder in an organic solvent containing a peeling accelerator consisting of an alkali metal or alkaline earth metal and a hydroxyl group; And it provides a method for producing molybdenum disulfide (MoS2) nanosheets comprising the step of producing a molybdenum disulfide (MoS2) nanosheets by sonicating the mixed bulk molybdenum disulfide (MoS2) powder.

In one embodiment of the present invention, the organic solvent is N-methyl pyrrolidone (NMP), the molybdenum disulfide (MoS2) nanosheets the production yield increases with the sonication time.

In one embodiment of the present invention, the release promoter is sodium hydroxide.

The present invention also provides molybdenum disulfide (MoS2) nanosheets prepared by the method described above, wherein the molybdenum disulfide (MoS2) nanosheets comprise 1-3 layers of nanosheets at least 85% of the total nanosheets.

The present invention also provides a peeling accelerator comprising an alkali metal or alkaline earth metal and a hydroxyl group; And an organic solvent, wherein the molybdenum disulfide (MoS 2) stripping solution is provided, wherein the organic solvent is N-methyl pyrrolidone (NMP), and the stripping accelerator is sodium hydroxide.

According to the present invention, when MoS2 is mixed and sonicated in a stripping solution in which a basic solution is added to an organic solvent, it is possible to peel MoS2 with a remarkably short ultrasonic decomposition time, and shows a yield of about 6 times MoS2 nanosheets. MoS2 can be produced in an economical and efficient manner. In addition, the stripper and the process according to the invention allow for the production of large quantities of MoS ₂ nanosheets with a single and small number of layers.

Figure 1 is a) SEM image of the original MoS2 powder (B) Schematic diagram of the structure of MoS ₂ (C) SEM image showing the effect of the addition of NaOH (right, Example) SEM showing the result of not adding NaOH It is an image (left, comparative example).

FIG. 2A is a UV-vis and photoluminescence spectrum (insertion: photographic image of dispersed MoS ₂ ), 2B is an SEM image of MoS2 nanosheets peeled off by adding NaOH to NMP.

3A to E are TEM images of MoS ₂ nanosheets, 3F is a tapping-mode AFM image, and 3G is the corresponding line scan results of MoS2-nanosheets on a silicon substrate.

Fig. 4 (A) Raman spectrum, (B) XPS spectrum of Mo 3d and (C) S 2p of MoS 2 nanosheet film on SiO ₂ / Si substrate. (D) XRD pattern of MoS2 bulk powder, MoS2 nanosheet with NaOH, and nanosheet without NaOH.

Figure 5 (A) is a charge-discharge curve, (B) is a graph showing the Coulomb efficiency and cycle number.Sodiation and Desodiation capacity in coin-type half cells at room temperature.

Experimental examples introduced below are provided as examples to ensure that the spirit of the present invention to those skilled in the art can be sufficiently delivered. Therefore, the present invention is not limited to the experimental examples described below and may be embodied in other forms. In addition, the abbreviations shown throughout this specification should be interpreted to the level understood in the art, unless otherwise indicated herein.

MEANS TO SOLVE THE PROBLEM The present inventor solved the problem of the prior art mentioned above, the outstanding workability to a surrounding environment, the problem of phase transition does not arise, and the high yield molybdenum disulfide (MoS2) nanosheet peeling liquid and its peeling liquid which shortened the process time of an ultrasonic wave. It provides a method for producing MoS2 nanosheets.

To this end, the present invention uses an organic solvent containing a compound consisting of an alkali metal or an alkaline earth metal and a hydroxyl group (hereinafter, a peeling accelerator) as a stripping solution, and incorporates molybdenum disulfide (MoS 2) powder in bulk from the stripping solution. Sonication to prepare molybdenum disulfide (MoS2) nanosheets. In particular, a mixture of a solvent having high dielectirc strength with respect to MoS2 such as N-methyl pyrrolidone (NMP) and a release accelerator containing a hydroxyl group and an alkali or alkaline earth metal such as NaOH is used. The present invention provides an economical method for stripping nanosheets of MoS2 from the new fact that the penetration of Na + and OH- ions into the space inside the layer of MoS2 is easy.

MoS2 Nanosheet Dispersion

First, NaOH (5 g) was dissolved in NMP (20 mL), and MoS 2 bulk powder (20 mg) was added to NaOH solution. The mixture was sonicated in an sonicator for 2 hours. For the control experiment, a mixed solution under the same conditions but without addition of NaOH was used.

Experiment result

Figure 1 is a) SEM image of the original MoS2 powder (B) Schematic diagram of the structure of MoS ₂ (C) SEM image showing the effect of the addition of NaOH (right, Example) SEM showing the result of not adding NaOH It is an image (left, comparative example).

In this experimental example, the mixed solution was sonicated for 2 hours in a bath sonicator, and in the comparative example, a peeling solution to which a basic solution such as NaOH was not added was used.

After the sonication for 2 hours, the separation solution of Example or Comparative Example was centrifuged at 2000 rpm for 30 minutes using a centrifuge (Hanil Industrial Co., Ltd., Combi 514R), and the precipitate was not stripped of MoS _2. Or discarded to remove thick pieces.

For the MoS ₂ release film of the supernatant obtained third, the inner layer space of the MoS ₂ nanosheets with a vacuum filter using anodized aluminum oxide (AAO) (Anodisc 47, 0.025 μm pores, Whatman) Was analyzed. The remaining supernatant with or without NaOH was centrifuged at 9000 rpm for 45 minutes, the supernatant was discarded and fresh NMP solvent was added.

The solution was then sonicated for 3 minutes and centrifuged at 9000 rpm for 45 minutes to remove most of the NaOH. The washing process was repeated several times to obtain a clean solution with NaOH. The pH of the supernatant was measured using pH test paper to confirm the removal of NaOH after each centrifugation. After centrifugation, the volume of precipitate added with NaOH was much larger than that without NaOH (FIG. 1C). In addition, compared to the peeling solution of the comparative example, the peeling solution of the Example increased the yield of MoS2 nanosheets to about 6 times. From the above results, it can be seen that under the ultrasonic process, NaOH added to the stripping solution contributes to stripping the MoS ₂ layers, and as a result, the concentration of the stripped MoS ₂ sheet is significantly improved. In addition, as the sonication time was increased, its concentration increased. When the sonication time was longer, the dispersion efficiency of MoS ₂ added with NaOH was very high. This also means that NaOH facilitates the exfoliation of MoS ₂ bulk pieces.

After the wash, further sonication for 40 minutes gave the final MoS ₂ dispersion. The final obtained solution between 2000 rpm and 9000 rpm was dark green and remained stable for several days without aggregation.

In order to characterize the final solution by UV-vis spectrophotometer, it was used to prepare MoS2 thin film on SiO ₂ / Si substrate by drop casting method, and the nanosheets were characterized by SEM and photoluminescence.

FIG. 2A is a UV-vis and photoluminescence spectrum (insertion: photographic image of dispersed MoS ₂ ), 2B is an SEM image of MoS2 nanosheets peeled off by adding NaOH to NMP.

Referring to FIG. 2A, the spectrum of the MoS2 nanosheets dispersed using the stripper according to the present invention shows two peaks (A and B) between 600 nm and 700 nm, and a broad band near 450 nm having a shoulder at 399 nm. Also indicated. A and B peaks are characteristic of 2H-MoS ₂ nanosheets and correspond to the fewest direct transitions. At this time, the peak positions of the excitons of A and B are 670 nm (1.85 eV) and 607 nm (2.04 eV), and there is an energy difference of 0.19 eV. The exciter values show a blue shift compared to known data for bulk powder (748 nm (1.66 eV)). The blue shift is due to the quantum-size confinement, which is consistent with previous studies.

Also, referring to FIG. 2B, the MoS ₂ thin film on the SiO ₂ / Si substrate is clearly shown to be 2D pieces having a base plate and an edge.

The inventors examined the dispersion of MoS ₂ nanosheets through TEM analysis, and FIG. 3 shows TEM images of several layers of MoS ₂ nanosheets on a Holy carbon TEM grid.

Referring to FIG. 3, TEM images of MoS ₂ nanosheets generally appear as wrinkled sheets partially folded like graphene sheets, and HRTEM images of MoS ₂ nanosheets (see FIG. 3E) show very clear edges.

This was obtained with the part indicated by the black circle as shown at the bottom left of FIG. 3D, and the inserted part of FIG. 3E shows a typical electron diffraction pattern of the exfoliated MoS ₂ .

The AFM image provides additional information on the thickness of the single layer and the efficient exfoliation of the MoS ₂ nanosheets. Through AFM analysis, the inventors found an association between the morphology and the thickness of the nanosheet film.

3F and G show the AFM image and layer height of a single layer MoS ₂ nanosheet on a SiO ₂ / Si substrate.

Referring to Figures 3F and G results, the layer height of the nanosheets was measured at 1.2 nm. This thickness is quite consistent with the results of previous studies on single layer MoS ₂ in liquid stripping.

According to the TEM and AFM images obtained from the above results, it can be seen that the lateral dimension of the nanosheets ranges from 50 nm to 1 μm. In addition, single layer MoS ₂ nanosheets exhibit lateral lengths less than 300 nm.

Raman spectra provide easy and qualitative characterization of MoS ₂ nanosheets.

Fig. 4 (A) Raman spectrum, (B) XPS spectrum of Mo 3d and (C) S 2p of MoS 2 nanosheet film on SiO ₂ / Si substrate. (D) XRD pattern of MoS2 bulk powder, MoS2 nanosheet with NaOH, and nanosheet without NaOH.

Referring to FIG. 4, a typical peak known as the E ¹ _2g peak at 385.6 cm ⁻¹ originates from the planar vibration of Mo-S and a non-planar vibration is observed in the A _1g peak near 408 cm ⁻¹ . The spectrum of the original MoS ₂ powder shows peaks at 383 and 409 cm ⁻¹ . The peak difference between E ¹ _2g and A _1g is 26 cm ⁻¹ for the original MoS ₂ , but 22.4 cm ⁻¹ for the MoS ₂ dispersion prepared according to the invention. In other words, the numerical value of the MoS ₂ dispersion according to the present invention is smaller than that of the original MoS ₂ powder. This peak difference can be used to measure the number of MoS ₂ layers, the peak difference of 22.4 cm ⁻¹ of the MoS ₂ dispersion according to the invention corresponding to the MoS ₂ trilayer structure. In addition, the line widths (6 to 7 cm ^-1 ) for the MoS2 dispersions according to the invention are larger than the known data (2 to 6 cm ^-1 ) of MoS ₂ single crystals by the mechanical exfoliation method. The line broadening is due to the smaller crystal size and larger defects compared to the MoS ₂ single crystals of previous studies, including the liquid stripping method.

The three-layer MoS ₂ nanosheets are clearly seen in the PL spectrum of FIG. 2 (A) (red line). The PL spectrum consists of one main peak near 665 nm (1.86 eV) and one shoulder peak at 614 nm. And it fits well with the exciton energy from the direct band gap PL, which is in good agreement with the known data.

The inventors then made an XPS measurement, which is shown in FIGS. 4 (B)-(D).

In FIG. 4B, the Mo 3d peak corresponds to Mo ⁴⁺ 3d5 / 2 (229.3 eV) and Mo ⁴⁺ 3d3 / 2 (232.6 eV), which are expected values for Mo ⁴⁺ in MoS ₂ . The corresponding S 2p peak consists of one double term of 2p ^1/2 (163.4 eV) and S 2p3 / 2 (162.3 eV). This is consistent with the S ² -form in MoS ₂ . (Fig. 4 (C)) This shows a small peak around 236 eV, corresponding to Mo ⁶⁺ 3d5 / 2 of Mo oxidation.

In the exfoliation experiment according to the present invention, NaOH facilitates exfoliation of MoS ₂ pieces, i.e., to characterize the intercalation of NaOH in the MoS ₂ nanosheets, the inventors made XRD (X-ray diffraction) measurements and the original MoS It was compared with that of the film peeled off from NMP without ₂ powder and NaOH addition, which can be seen in FIG. 4 (D).

The XRD peak of the (002) crystal plane of the relaminated MoS ₂ film in the NMP solution without adding NaOH has the same pattern as the peak of the (002) crystal plane of the original MoS ₂ powder. This implies that the space of the inner layer of MoS ₂ has not changed due to the treatment in NMP and that there is no effect on NMP molecules for intercalation to MoS ₂ inner layer. However, it can be seen that the re-laminated film of MoS ₂ subjected to NaOH treatment shifts the peak of the (002) crystal plane below nighttime. The peak indicates that the interlayer space of the film was partially expanded due to the addition of NaOH at the low diffraction angle of the (002) crystal plane peak. As mentioned in the XPS analysis of Mo oxidation, a small peak of Mo oxidation was analyzed as Na ₂ MoO ₄ in the XRD spectrum, and no peak was found around 168 eV for the oxidized sulfur atom.

In conclusion, the exfoliated MoS ₂ nanosheets exhibited the electrochemical properties of the anode material of sodium-ion batteries.

Figure 5 (A) is a charge-discharge curve, (B) is a graph showing the Coulomb efficiency and cycle number.Sodiation and Desodiation capacity in coin-type half cells at room temperature.

Referring to FIG. 5, the charging and discharging curves are shown at a current density of 20 mA g ⁻¹ . Two ballasts were observed at 0.94 V and 0.84 V on the first sodiation curve, and four ballasts were observed at 1.3, 1.6, 2.3, and 2.5 V on the first desodiation curve. From the second cycle, the Sodiation and Desodiation curves change from the stable of the first curve to the sloped curve.

Sodiation capacity gradually decreases as the cycle repeats, and after 45 cycles the capacity reaches 96 mA hg ^-1 . (Fig. 5 (B))

As described above, the inventors peeled MoS2 monolayer sheets very quickly in an organic solvent such as NMP containing a release promoter. In particular, when a solvent having high dielectirc strength with respect to MoS2, such as NMP, and a release accelerator containing a hydroxyl group and an alkali metal or an alkaline earth metal, such as NaOH, Na + is easily used as a space inside the layer of MoS2. And the penetration of OH- ions becomes easy. As a result, NaOH in the ultrasonic conditions help the easy peeling of the MoS2 layer, despite the short reaction time, it is possible to obtain a sufficient concentration of MoS2 nanosheet dispersion. The MoS2 sheet obtained has mainly a single layer or several layer thicknesses. Therefore, the present invention can mix MoS2 by using a basic solution such as NaOH in an organic solvent such as NMP, thereby producing MoS2 nanosheets in an economical and efficient manner.

Claims (8)

Incorporating bulk molybdenum disulfide (MoS 2) powder into an organic solvent containing a peeling accelerator comprising an alkali metal or an alkaline earth metal and a hydroxyl group; And Molybdenum disulfide (MoS2) nanosheet manufacturing method comprising the step of producing a molybdenum disulfide (MoS2) nanosheets by sonicating the mixed bulk molybdenum disulfide (MoS2) powder. The method of claim 1, The organic solvent is N-methyl pyrrolidone (Methyl pyrrolidone, NMP), characterized in that the molybdenum disulfide (MoS2) nanosheet manufacturing method. The method of claim 1, The molybdenum disulfide (MoS2) nanosheets manufacturing method characterized in that the production yield increases with the sonication time. The method of claim 1, The release promoter is molybdenum disulfide (MoS2) nanosheets manufacturing method characterized in that the sodium hydroxide. Molybdenum disulfide (MoS2) nanosheets prepared by the method according to any one of claims 1 to 4. The method of claim 5, The molybdenum disulfide (MoS2) nanosheets are molybdenum disulfide (MoS2) nanosheets, characterized in that 1 to 3 nanosheets are 85% or more of the total nanosheets. Peel accelerators composed of alkali or alkaline earth metals and hydroxyl groups; And Molybdenum disulfide (MoS2) stripping liquid containing an organic solvent. The method of claim 7, wherein The organic solvent is N-methyl pyrrolidone (NMP), molybdenum disulfide (MoS2) stripping liquid, characterized in that the peeling accelerator is sodium hydroxide.

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