A method for preparing two-dimensional molybdenum disulfide quantum dots based on cyclic ultrasonic atomization

Abstract

The application discloses a method for preparing two-dimensional molybdenum disulfide quantum dots based on cyclic ultrasonic atomization, which uses commercial molybdenum disulfide powder as raw material and tetrabutylammonium tetrafluoroborate as intercalation agent, and disperses the raw material in a mixed solvent of deionized water and propylene carbonate to form a suspension; the suspension is dispersed into micron-sized droplets through cyclic ultrasonic atomization, and a high-voltage direct current electric field is applied to charge the droplets to form charged microdroplets; the interfacial electric field effect, confined mass transfer effect and ammonium salt ion intercalation effect of the charged microdroplets are used to synergistically promote the interlayer exfoliation of molybdenum disulfide; after cyclic reaction, two-dimensional molybdenum disulfide quantum dots are obtained through centrifugation, filtration and dialysis purification. The application realizes one-step conversion of molybdenum disulfide powder into uniform quantum dots at normal temperature and pressure, has the advantages of simple process, mild reaction conditions, high raw material utilization rate and narrow size distribution of products, and is suitable for large-scale preparation of two-dimensional molybdenum disulfide quantum dots.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional nanomaterial preparation and microdroplet technology, specifically relating to a method for preparing two-dimensional molybdenum disulfide quantum dots (2D-MoS2QDs) based on cyclic ultrasonic atomization microdroplet technology. Background Technology

[0002] Two-dimensional molybdenum disulfide quantum dots (2D-MoS2QDs) possess significant edge effects, quantum confinement effects, and unique optical and electronic properties, showing promising applications in fluorescence sensing, bioimaging, photocatalysis, optoelectronic devices, and energy conversion. Developing a simple, low-cost method for synthesizing 2D-MoS2QDs that enables controllable and uniform preparation is crucial for promoting their further applications.

[0003] Currently, the preparation methods for MoS2 quantum dots mainly fall into two categories: bottom-up and top-down methods. Bottom-up methods primarily involve the chemical reaction between molybdenum and sulfur source precursors to form MoS2 quantum dots, with hydrothermal and solvothermal methods being the most common. These methods typically require high temperature and high pressure conditions, have long reaction times, and involve multiple steps such as precursor preparation, reaction, washing, and purification. The process is relatively complex, sensitive to reaction parameters, and difficult to achieve continuous and large-scale preparation.

[0004] The top-down approach uses bulk MoS2 or MoS2 powder as raw material, breaking the interlayer forces through mechanical, physical, or chemical actions to gradually exfoliate and further reduce its size. Among these methods, liquid-phase ultrasonic exfoliation has attracted widespread attention due to its advantages such as lower equipment requirements, simple operation, and potential for large-scale preparation. However, existing liquid-phase ultrasonic exfoliation methods can usually only exfoliate bulk MoS2 into few-layer MoS2 nanosheets. The resulting products typically have lateral dimensions in the range of tens to hundreds of nanometers, with a wide distribution in both thickness and lateral size. It is difficult to directly obtain two-dimensional MoS2 quantum dots with lateral dimensions of approximately several nanometers and a uniform size distribution.

[0005] To further improve the degree of exfoliation and quantum dot yield, existing technologies often employ strong oxidation etching, chemical cutting, or prolonged high-power ultrasound for further fragmentation. However, strong oxidation conditions can easily introduce more defects or oxidation products into the MoS2 lattice, damaging the structural integrity of the product. Prolonged high-power ultrasound, on the other hand, suffers from high energy consumption and low efficiency.

[0006] Salt-assisted liquid-phase exfoliation is a common method to promote the exfoliation of layered MoS2. It utilizes the interaction between electrolyte ions and the interlayer or surface of MoS2 to reduce interlayer interactions and assist in material exfoliation, which can improve the yield efficiency of few-layer MoS2 nanosheets to some extent. However, existing salt-assisted liquid-phase exfoliation methods usually still require long periods of mechanical stirring, ultrasonication, or other external forces, resulting in problems such as long processing time, limited quantum dot yield, and uneven product size distribution. At the same time, the limited mass transfer efficiency of reactants in traditional batch liquid-phase systems also restricts further improvement in exfoliation efficiency and preparation reproducibility.

[0007] In recent years, microdroplet technology has attracted attention in the fields of accelerating chemical reactions and preparing nanomaterials due to its high specific surface area, short mass transfer distance, and unique interfacial chemical environment. Compared with traditional bulk solutions, microdroplet systems can provide a more significant liquid-gas interface, characterized by rapid solvent evaporation, rapid mass transfer, and interfacial enrichment, offering new reaction environments for regulating chemical reactions and material formation processes. Among these, microdroplets formed by ultrasonic atomization can achieve rapid dispersion and recycling of liquid-phase systems, providing a new technical approach to improve material preparation efficiency. Furthermore, when microdroplets undergo charge separation and carry a certain charge during formation and transport, a local electric field environment can be formed at their interface, providing new driving forces for ion migration, interfacial reactions, and the exfoliation of layered materials.

[0008] However, existing technologies lack a method for directly preparing uniformly sized 2D-MoS2 QDs that combines cyclic ultrasonic atomization, microdroplet charging effect, and ammonium salt-assisted intercalation exfoliation. How to utilize a cyclic microdroplet system to enhance the interfacial contact and mass transfer process between MoS2 and ammonium salt, and achieve efficient exfoliation and further size reduction of MoS2 while avoiding strong oxidation conditions and prolonged high-power ultrasonic treatment, remains a pressing technical problem to be solved in this field. Summary of the Invention

[0009] This invention addresses the problems of harsh preparation conditions, complex processes, long exfoliation times, wide product size distribution, and low raw material utilization in existing 2D-MoS2QDs preparation methods. It provides a one-step preparation method for 2D-MoS2QDs based on cyclic ultrasonic atomization and charged microdroplet technology, which achieves efficient and low-cost preparation of molybdenum disulfide quantum dots with uniform size under ambient temperature and pressure conditions.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing two-dimensional molybdenum disulfide quantum dots based on cyclic ultrasonic atomization, comprising the following steps: S1. Raw material dispersion: Molybdenum disulfide powder and tetrabutylammonium tetrafluoroborate are added to a mixed solvent of deionized water and propylene carbonate, and dispersed evenly by magnetic stirring or ultrasonication to obtain a stable suspension.

[0011] S2. Circulating ultrasonic atomization: The suspension is introduced into a closed circulating ultrasonic atomization reactor, and a condensate circulation jacket is provided on the outer wall of the reactor. The suspension is torn into a large number of micron-sized highly dispersed droplets by high-frequency ultrasonic vibration. During the rise of the droplets, some of them are condensed and refluxed. The unreacted molybdenum disulfide particles are re-entered into the bottom atomization area with the reflux liquid to achieve circulating atomization treatment.

[0012] S3. Electric Field Charging and Synergistic Stripping: Platinum wire electrodes are set in the atomizing reactor and connected to a high-voltage DC power supply to form a high-voltage DC electric field inside the reactor. During the transport process, the droplets pass through the electric field region, and the surface is enriched with net charge to form charged microdroplets. Under the synergistic effect of electric field driving and microdroplet confinement effect, the tetrabutylammonium tetrafluoroborate ions in the charged microdroplets rapidly diffuse and insert into the molybdenum disulfide interlayer, weakening the interlayer van der Waals forces, promoting interlayer stripping and lateral size fragmentation, and finally generating a reaction liquid containing two-dimensional molybdenum disulfide quantum dots.

[0013] S4. Separation and purification: The reaction solution is transferred to a centrifuge tube for centrifugation to remove large particles that have not been separated. The supernatant is then filtered through a microfiltration membrane to remove impurities and transferred to a dialysis bag for dialysis purification to finally obtain a pure two-dimensional molybdenum disulfide quantum dot solution.

[0014] Further, in step S1, the molybdenum disulfide powder is commercially available bulk molybdenum disulfide powder, and the amount added is 0.1~0.2g per 100mL of mixed solvent; the concentration of the tetrabutylammonium tetrafluoroborate is 0.03~0.08mol / L; and the volume ratio of deionized water to propylene carbonate is 1:(0.8~1.2).

[0015] Furthermore, in step S2, the ultrasonic atomization operates at a frequency of 2.0~2.8MHz and has a rated power of 15~25W; the total duration of the cyclic atomization treatment is 1~3h.

[0016] Furthermore, in step S3, the platinum wire electrode is immersed in the liquid phase region at the bottom of the reactor, the negative terminal of the high-voltage DC power supply is connected to the platinum wire electrode, and the metal shell of the reactor is grounded to form an electric field circuit; the applied DC voltage is -3~-5kV.

[0017] Further, in step S4, the centrifugation speed is 8000~12000 rpm and the centrifugation time is 5~10 min; the microfiltration membrane is an organic microporous membrane with a pore size of 0.22 μm; the dialysis purification is performed by dialyzing with deionized water 3 times and with anhydrous ethanol 3 times in sequence, with each dialysis lasting no less than 6 hours.

[0018] The two-dimensional molybdenum disulfide quantum dots prepared by the above method have a thickness of about 0.7 nm (corresponding to the thickness of a single layer of molybdenum disulfide), and the lateral size is mainly distributed in the range of 2~5 nm, with narrow size distribution and good uniformity.

[0019] Compared with the prior art, the present invention has the following advantages: 1. This invention is carried out under normal temperature and pressure conditions, using commercial MoS2 powder as raw material. It achieves size reduction and interlayer exfoliation of MoS2 through ultrasonic atomization, microdroplet charging and ammonium salt-assisted exfoliation. It does not require a high temperature and high pressure reactor, nor does it require strong oxidation etching or long-term mechanical stirring. It is simple to operate and has low equipment requirements.

[0020] 2. This invention can precisely control the degree of molybdenum disulfide exfoliation through the synergistic effect of microdroplet confinement, electric field-driven ion intercalation, and cyclic processing. Under preferred conditions, the lateral size of the obtained 2D-MoS2QDs is concentrated in the range of 2~5nm, and the thickness is about 0.7nm. The size uniformity is good, which can meet the high requirements for the size distribution of nanomaterials in fields such as fluorescence sensing and bioimaging.

[0021] 3. The present invention adopts a circulating atomization structure, and the MoS2 particles that are not fully stripped can re-enter the atomization and reaction zone for repeated processing, increasing the effective processing times of raw materials and improving the utilization rate of raw materials; at the same time, the liquid phase medium is recycled, reducing solvent consumption and lowering the material cost of the preparation process.

[0022] 4. This invention uses inexpensive and readily available commercial molybdenum disulfide powder as raw material, and combines it with water, propylene carbonate and quaternary ammonium salt to construct a reaction system. It does not rely on complex precursor synthesis processes, and the overall preparation cost is significantly lower than that of bottom-up synthesis methods.

[0023] 5. The method of the present invention is based on ultrasonic atomization and cyclic reaction mode, does not rely on intermittent high-pressure reaction equipment, and can achieve scale-up of processing by increasing the reactor volume and connecting multiple atomization units in parallel, and has the potential for continuous production modification. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the experimental process and apparatus for preparing 2D-MoS2QDs using cyclic ultrasonic atomization technology according to the present invention.

[0025] Figure 2 The images show transmission electron microscopy (TEM) images and particle size distributions of the MoS2QDs prepared in Example 1 of this invention.

[0026] Figure 3 High-resolution scanning tunneling microscope (STM) images and height profiles of the 2D-MoS2QDs prepared in Example 1 of this invention.

[0027] Figure 4 The image shows a TEM image of the MoS2 product obtained in Comparative Example 1 (nebulization for 30 min).

[0028] Figure 5 The image shows the STM image and corresponding height profile of the MoS2 product obtained in Comparative Example 2 (without an applied DC voltage). Detailed Implementation

[0029] The present invention will be further described below.

[0030] Example 1: Preparation of 2D-MoS2QDs using a circulating ultrasonic atomization device, the specific steps are as follows: S1. Raw material dispersion: Weigh 0.15g of commercial MoS2 powder, measure 100mL of a mixed solvent of deionized water and propylene carbonate (volume ratio 1:1), add tetrabutylammonium tetrafluoroborate to a concentration of 0.05mol / L; stir magnetically for 30min and then ultrasonically disperse for 10min to obtain a uniform and stable suspension.

[0031] S2. Device Setup: A closed atomizing reactor made of double-layered glass is used. The reactor has an inner diameter of 8.5cm, an outer diameter of 11cm, and a height of 14cm. Cooling water is circulated through the jacket for droplet condensation and reflux. An ultrasonic atomizing plate is installed at the bottom of the reactor, operating at a frequency of 2.4MHz and a rated power of 21W. A platinum wire electrode is inserted from the top of the reactor, with its lower end immersed in the bottom liquid phase region. The platinum wire electrode is connected to the negative terminal of a high-voltage DC power supply, and the reactor's metal base is grounded.

[0032] S3. Circulating Atomization and Electric Field Stripping: The suspension is added to the atomizing reactor, the condensate circulation is started, and the ultrasonic atomizer is activated. Under high-frequency vibration, the suspension is torn into a large number of micron-sized droplets. During the rise of the droplets, they condense in the condensation interlayer, carrying incompletely stripped MoS2 particles back to the bottom liquid phase zone along the reactor wall, and re-enter the atomization area, forming a circulating process. Simultaneously, the high-voltage DC power supply is turned on, and the output voltage is set to -4kV to create a DC electric field inside the reactor. When the droplets pass through the electric field region, their surfaces are enriched with negative charges, forming charged microdroplets. Under the synergistic effect of electric field driving and microdroplet confinement effect, tetrabutylammonium tetrafluoroborate ions rapidly diffuse and insert into the MoS2 interlayer, promoting interlayer stripping and size fragmentation. The total duration of the circulating atomization reaction is 2 hours, yielding a reaction solution containing 2D-MoS2 QDs.

[0033] S4. Separation and Purification: Add 10 mL of the reaction solution to a 10 mL centrifuge tube and centrifuge at 10,000 rpm for 8 min to remove large, unremoved MoS2 precipitates. Collect the supernatant. Filter the supernatant through a 0.22 μm microporous membrane and transfer it to a dialysis bag with a molecular weight cutoff of 1000 Da. Dialyze three times with deionized water and three times with anhydrous ethanol, each dialysis session lasting 8 hours, with the dialysis solution replaced every 6 hours. After dialysis, collect the solution in the dialysis bag; this is the purified two-dimensional molybdenum disulfide quantum dot solution.

[0034] Example 2: Structural and morphological characterization of 2D-MoS2QDs: Transmission electron microscopy (TEM) characterization: The purified quantum dot solution prepared in Example 1 was dropped onto the surface of a copper mesh coated with an ultrathin carbon film, gently rinsed three times with anhydrous ethanol, and allowed to air dry before TEM testing. The results are as follows: Figure 2 As shown, the obtained product consists of well-dispersed nanoparticles with a statistically average particle size of approximately 3 nm, a narrow size distribution, and no obvious agglomeration.

[0035] Scanning tunneling microscopy (STM) characterization: A mica-supported Au(111) crystal plane was used as the substrate. Quantum dot solution was drop-coated onto the Au(111) surface, allowed to air dry, rinsed three times each with ethanol and deionized water, dried with nitrogen, and then subjected to high-resolution STM testing. Results are as follows: Figure 3 As shown, the lateral dimensions of the quantum dots are 2-5 nm. A height profile was drawn along the white line segment in the figure, and the height of the quantum dots was measured to be approximately 0.7 nm, which is consistent with the theoretical thickness of monolayer molybdenum disulfide, proving that the obtained product is a monolayer two-dimensional molybdenum disulfide quantum dot.

[0036] Comparative Example 1 (Shortened Atomization Time): The total atomization time was shortened to 30 min, while the remaining raw material ratios, atomization parameters, electric field conditions, and post-treatment steps were exactly the same as in Example 1. The obtained product was characterized by TEM, and the results are as follows: Figure 4 As shown, the product contains only a very small number of small-sized quantum dots, with most particles larger than 50 nm, remaining in a nanosheet morphology. This result indicates that sufficient cycling time is a necessary condition for achieving complete exfoliation and obtaining quantum dots of uniform size.

[0037] Comparative Example 2 (No External Electric Field): The high-voltage DC power supply was disconnected, and no external electric field was applied. All other raw material ratios, atomization parameters, processing time, and post-processing steps were exactly the same as in Example 1. The obtained product was characterized by STM, and the results are as follows: Figure 5 As shown, the product particle size is approximately 100 nm, and no quantum dot-scale products were formed. This result indicates that the charged microdroplet effect induced by the applied electric field plays an indispensable role in driving ion intercalation and promoting interlayer exfoliation.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing two-dimensional molybdenum disulfide quantum dots based on cyclic ultrasonic atomization, characterized in that, Includes the following steps: (1) Raw material dispersion: Molybdenum disulfide powder and tetrabutylammonium tetrafluoroborate were added to a mixed solvent of deionized water and propylene carbonate and dispersed evenly to obtain a suspension; (2) Circulating ultrasonic atomization: The suspension is introduced into a closed circulating ultrasonic atomization reactor. The suspension is torn into micron-sized droplets by high-frequency ultrasonic vibration. The unreacted material is re-entered into the atomization area with the condensed reflux liquid to achieve circulating atomization treatment. (3) Electric field charging and synergistic stripping: A high-voltage DC electric field is applied in the atomizing reactor so that the droplets carry net charge during transport to form charged microdroplets; under the synergistic effect of electric field driving and microdroplet confinement effect, the tetrabutyltetrafluoroborate ions in the charged microdroplets insert into the molybdenum disulfide interlayer, promoting interlayer stripping and size fragmentation, and generating a reaction liquid containing two-dimensional molybdenum disulfide quantum dots; (4) Separation and purification: The reaction solution is separated by centrifugation, the supernatant is filtered through a microfiltration membrane, and then purified by dialysis to obtain two-dimensional molybdenum disulfide quantum dots.

2. The method according to claim 1, characterized in that, In step (1), the amount of molybdenum disulfide powder added is 0.1~0.2g per 100mL of mixed solvent; the concentration of tetrabutylammonium tetrafluoroborate is 0.03~0.08mol / L; and the volume ratio of deionized water to propylene carbonate is 1:(0.8~1.2).

3. The method according to claim 2, characterized in that, In step (1), the amount of molybdenum disulfide powder added is 0.15g per 100mL of mixed solvent; the concentration of tetrabutylammonium tetrafluoroborate is 0.05mol / L; and the volume ratio of deionized water to propylene carbonate is 1:

1.

4. The method according to claim 1, characterized in that, In step (2), the ultrasonic atomization operates at a frequency of 2.0~2.8MHz and has a rated power of 15~25W; the total duration of the cyclic atomization process is 1~3h.

5. The method according to claim 4, characterized in that, In step (2), the ultrasonic atomization operates at a frequency of 2.4 MHz and has a rated power of 21 W; the total duration of the cyclic atomization process is 2 hours.

6. The method according to claim 1, characterized in that, The high-voltage DC electric field is applied through a platinum wire electrode immersed in the liquid phase zone of the reactor, with an applied voltage of -3 to -5 kV; the platinum wire electrode is connected to the negative terminal of the high-voltage DC power supply, and the reactor shell is grounded to form an electric field loop.

7. The method according to claim 6, characterized in that, In step (3), the applied voltage is -4kV.

8. The method according to claim 1, characterized in that, The centrifugation speed is 8000~12000 rpm, and the centrifugation time is 5~10 min; the pore size of the microfiltration membrane is 0.22 μm.

9. The method according to claim 1, characterized in that, The dialysis purification process involves three dialysis cycles with deionized water and three dialysis cycles with anhydrous ethanol, with each dialysis cycle lasting no less than 6 hours.

10. The method according to any one of claims 1 to 9, characterized in that, The thickness of the obtained two-dimensional molybdenum disulfide quantum dots is 0.6~0.8 nm, and the lateral dimension is 2~5 nm.

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