KR101212015B1 - Method for preparing II to VI group semiconductor compound quantum dot or nanoparticles through sonochemical method under multi-bubble sonoluminescence conditions, and method for controlling size of the quantum dot or the nanoparticles - Google Patents

Abstract

The present invention relates to a method for manufacturing a group II to VI semiconductor quantum dots or nanoparticles using ultrasonic emission method under multi-bubble sonic emission conditions and a method for controlling the size of the quantum dots or nanoparticles, Ultrasonic luminescence can be used to prepare high yield quantum dots of Group II-VI compounds through convenient and simple one-pot reactions without any pretreatment and / or high temperature conditions. In addition, the quantum dots may be calcined and converted into nanoparticles. In addition, there is an effect of controlling the size of the quantum dots or nanoparticles by controlling the sonication conditions or firing conditions.

Description

Method for preparing group II to VI semiconductor quantum dots or nanoparticles using ultrasonic emission method under multi-bubble sonic emission conditions and method for controlling the size of the quantum dots or nanoparticles nanoparticles through sonochemical method under multi-bubble sonoluminescence conditions, and method for controlling size of the quantum dot or the nanoparticles}

The present invention provides a method for producing quantum dots or nanoparticles of Group II to VI compounds using ultrasonic luminescence under multi-bubble sonic emission conditions and controlling the size of the quantum dots or nanoparticles by controlling the sonication or firing conditions. It is about a method.

Alloyed semiconductor quantum dots have been widely studied for their versatile and widespread use, and many researchers have focused on various adjustable properties depending on their particle size. They exhibit varying color and photoluminescence properties, mainly due to their quantum confinement effects, in their size changes. Thus, these quantum dots have been used as absorbers in light emitting diodes, bioimaging, or solar cells. Among II-VI semiconductor quantum dots, CdSe or CdTe has strong photoluminescence and bulk CdTe is used for solar cell energy conversion. This is because it has a direct optical band gap of 1.44 eV, which is almost optimally matched to the solar spectrum. Well dispersed CdTe quantum dots can be deposited by spin-coating, layer by layer, or dip-coating methods. Most of their synthesis methods using pyrophoric organometallic precursors use Cd (CH ₃ ) ₂ as the reactant, which is difficult to handle and harmful. Non-pyrophoric reactants, such as CdO or Cd (Ac) ₂ , utilize solvents with high boiling temperatures, so typical reaction temperatures are about 300 ° C. In the case of high temperature reactions, it is rather difficult to control the crystal growth because the reaction occurs quickly. Growth can be terminated by obtaining an aliquot of the reaction mixture during the reaction or by adding a cold reaction terminating solvent. In addition, traditional aqueous solution routes for the preparation of CdTe nanocrystals using thiol ligands as capping agents are usually time consuming and have reported little luminescent properties in dark red to near-infrared emitting windows.

On the other hand, the sonic luminescence (Sonoluminescence, SL) phenomenon using the ultrasonic wave is a phenomenon in which the air bubbles in the liquid is synchronized with the ultrasonic wave to emit light when the vibrating gas bubbles suddenly contracted. In other words, if the ultrasonic wave is applied to the air bubbles in the liquid, the bubble contracts and expands repeatedly according to the cycle of the ultrasonic wave. Acoustic emission methods include single-bubble sonoluminescence and multi-bubble sonoluminescence. Acoustic emission by multi-bubbles is irradiated with high-energy sound waves, so many bubbles are generated and grow and contract almost simultaneously. Therefore, the use of multi-bubble sonic emission, which involves a lot of bubbles, it is possible to make good use of sonic emission phenomenon. When contracted around the bubble wall where multi-bubble sonic emission occurs, a liquid reaction zone with a high temperature of about 1,000 ° C. and a high pressure of about 500 bar is generated, and OH radicals are generated. In this reaction zone, high energy and high pressure environment and high reactive radicals make high energy chemical reaction possible. Even in bubbles, high-energy chemical reactions are possible due to similar conditions, such as high temperatures and the generation of OH radicals.

However, there have been no reports of the manufacture of semiconductor quantum dots using sonic light emission by such multiple bubbles.

It is an object of the present invention to provide a method for producing semiconductor quantum dots or nanoparticles through a convenient and simple one-pot reaction without any pretreatment and / or high temperature conditions using the ultrasonic chemistry described above.

Another object of the present invention is to provide a method for controlling the size of the quantum dots or nanoparticles by adjusting the manufacturing process conditions, such as ultrasonic treatment conditions, firing conditions.

In order to achieve the above object,

Preparing a mixed solution of Group II-VI semiconductor precursors, surfactants, and dispersants in a polar or nonpolar solvent; And

It provides a method for producing a group II to VI semiconductor quantum dots or nanoparticles comprising the step of producing a semiconductor quantum dot by ultrasonication of the mixed solution in a multi-bubble sonoluminescence conditions.

The invention also provides for the preparation of group II to VI semiconductor quantum dots or nanoparticles by sonication under multi-bubble sonoluminescence conditions.

It provides a method for controlling the size of the group II to VI semiconductor quantum dots or nanoparticles comprising the step of controlling the ultrasonic treatment time, or controlling the firing conditions.

The present invention has the effect of producing high-purity colloidal semiconductor quantum dots of high yield through convenient and simple one-pot reaction without any pre-treatment and / or high temperature conditions by sonication in multi-bubble sonic emission conditions.

The present invention also has the effect of converting the colloidal semiconductor quantum dots into nanoparticles by firing.

In addition, the present invention has the effect of controlling the size of the quantum dots or nanoparticles by adjusting the sonication conditions, or the firing conditions.

Figure 1 shows the XRD pattern of CdTe quantum dots prepared in toluene solvent (a) and octadecene solvent (b) according to the method of the present invention.
2 shows an HR-TEM image (a) and an electron diffraction pattern (b) of a CdTe quantum dot of the present invention.
Figure 3 shows the image and size distribution of the CdTe quantum dot of the present invention.
Figure 4 is a photograph of the colloidal CdTe solution of the present invention obtained by ultrasonic treatment time under room light (a), UV-vis absorption spectrum of the CdTe quantum dots of the present invention by ultrasonic treatment time (b), by ultrasonic treatment time under UV lamp Photograph (c) of the colloidal CdTe solution of the present invention and the photoluminescence spectrum (excitation wavelength: 400 nm) (d) of CdTe quantum dots according to sonication time are shown.
Figure 5 shows the XRD pattern, TEM image and band gap of the CdTe particles obtained by firing the CdTe quantum dots of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, the structure of this invention is demonstrated concretely.

The present invention

Preparing a mixed solution of Group II-VI semiconductor precursors, surfactants, and dispersants in a polar or nonpolar solvent; And

The present invention relates to a method for manufacturing a group II to VI semiconductor quantum dots or nanoparticles, comprising the step of producing a semiconductor quantum dot by sonicating the mixed solution under multi-bubble sonoluminescence conditions.

In the method of the present invention, high purity group II to VI semiconductor quantum dots are prepared through simple one-pot reaction without pretreatment of semiconductor precursor and high temperature treatment by ultrasonic treatment under multi-bubble sonic emission conditions, and sintering the quantum dots to produce nanoparticles. Characterized in that.

The first step is to prepare a mixed solution of Group II-VI semiconductor precursors, surfactants, and dispersants in a polar or nonpolar solvent.

Specifically, the Group II to VI semiconductor precursors may use CdCl ₂ and Te or Se powder.

Since the present invention uses CdCl ₂ as a reactant for preparing semiconductor quantum dots, it is non-toxic and does not use a solvent having a high boiling point.

In addition, since Te or Se powder is directly mixed with the CdCl ₂ to react, there is no need for a pretreatment process for reducing Te to Te ^2- .

In addition, the surfactant may be a primary amine such as 1-hexadecylamine, octadecylamine, or 4- (2-aminoethyl) phenol {4- (2-aminoethyl) phenol}. It is recommended to use, but is not particularly limited thereto.

The dispersant may be an alkylphosphine series such as tripropylphosphine and tributylphosphine such that the Group II to VI semiconductor precursors are well dispersed on a polar or nonpolar solvent; Alkyl phosphite series such as triethyl phosphite and tributyl phosphite; Alternatively, alkylamine series compounds such as hexylamine, octylamine, dodecylamine, hexadecylamine and oleylamine can be used without limitation. More specifically, trioctylphosphine / trioctylphosphine oxide (TOP / TOPO) may be used. Most preferably, trioctylphosphine and trioctylphosphine oxide may be mixed in a molar ratio of 2: 3.

In addition, as the polar or non-polar solvent, a saturated hydrocarbon solvent such as hexane, cyclohexane, octane, decane, dodecane, hexadecane; Unsaturated hydrocarbon solvents such as hexene, cyclohexene, octene, dekene, dodekene, hexadekene, octadecene; Alcohol solvents such as methanol, ethanol, propanol, butanol and octanol; Aromatic hydrocarbon solvents such as benzene, chlorobenzene, dichlorobenzene and xylene; Or an aprotic polar solvent such as methylene chloride (MC), trichloroethylene (TCE), dimethylene formamide (DMF), dimethyl sulfoxide (DMSO) and the like can be used without limitation. More specifically, toluene or octadecene can be used.

In a second step, the II-VI semiconductor quantum dots may be manufactured by sonicating the mixed solution under multi-bubble sonic emission conditions.

The multi-bubble sound emission conditions can be implemented in a multi-bubble sound wave device including a conventional circulation bath. More specifically, it can be implemented using a frequency of 10 to 100 KHz and 100 to 500 W power while maintaining a temperature of 40 to 100 ° C. in an argon atmosphere. The pressure of the argon gas is preferably maintained at 0.5 to 2 atm.

The ultrasonic treatment is preferably performed for 5 to 40 minutes. When within the above range, it is possible to manufacture a high purity high yield group II to VI semiconductor quantum dots.

According to one embodiment, the color in the mixed solution is pale green when the Te slurry is completely dissolved in the solvent when less than 5 minutes of sonication. When the sonication time is more than 5 minutes, the color of the solution gradually changes from pale green to yellow to deep red. If the sonication time exceeds 40 minutes, no further color change in solution is observed. This suggests that the growth of group II to VI semiconductor quantum dots is completed.

The ultrasonic treatment time described above may affect the size of the semiconductor quantum dots. More specifically, when sonicated for 5 to 40 minutes, the size of the quantum dot may increase in size depending on time.

The quantum dots manufactured by the method of manufacturing the II-VI semiconductor quantum dots may be CdTe or CdSe.

The quantum dots prepared according to the method are present in the cubic phase without impurities, and may be specifically 2 to 10 nm in size.

In one embodiment, the XRD pattern exhibits broad peaks corresponding to the (111), (220), and (311) planes.

In addition, the method of manufacturing a group II to VI semiconductor quantum dots or nanoparticles of the present invention may further include the step of firing the semiconductor quantum dots converted to nanoparticles.

The semiconductor quantum dots manufactured in the above step are converted to nanoparticles while the size of the semiconductor quantum dots is increased and the characteristics of the quantum dots are lost.

The firing may be performed at 300 to 600 ° C. for 1 to 3 hours under vacuum.

The firing conditions described above may affect the size of the semiconductor nanoparticles. That is, the size of the nanoparticles in the firing conditions may be increased in size depending on the temperature and time.

The nanoparticles converted through the sintering are present in the cubic phase and may have a diameter of 12 nm to 10 μm. More specifically, it may be 12 to 30 nm.

The semiconductor quantum dots or nanoparticles prepared according to the method of manufacturing a group II to VI semiconductor quantum dots or nanoparticles of the present invention exhibit various color and photoluminescence characteristics according to various sizes, and the nanoparticles have a band gap of 1.53 eV. Photodetector, FRET-based biosensor, single-photon source, photoelectrode for water splitting, gas sensor, photocatalyst Photocatalyst). It can be used in a light emitting diode, a biological imaging agent, or an absorber of a solar cell.

The present invention also

In the preparation of group II to VI semiconductor quantum dots or nanoparticles by sonication under multi-bubble sonoluminescence conditions,

The present invention relates to a method for controlling the size of group II to VI semiconductor quantum dots or nanoparticles including controlling the sonication time or controlling firing conditions.

Ultrasonication time may affect the size of the synthesized quantum dots in the preparation of Group II to VI semiconductor quantum dots of the present invention. More specifically, when the ultrasonic treatment time is performed for 5 to 40 minutes, the size of the quantum dot is 2 to 10 nm, the longer the processing time becomes larger.

In addition, the quantum dots produced through the ultrasonic treatment may be converted into nanoparticles through firing. The firing conditions may affect the size of the nanoparticles. More specifically, the firing conditions may be carried out under vacuum at 300 to 600 ° C. for 1 to 3 hours, and the size of the nanoparticles prepared therefrom may have a diameter of 12 nm to 10 μm.

Hereinafter, the present invention will be described in more detail with reference to Examples of the present invention, but the scope of the present invention is not limited by the following Examples.

Example 1 Preparation of CdTe Quantum Dot in Toluene Solvent

Cadmium chloride (CdCl ₂ , 99.99%), tellurium powder (99.99%), trioctylphosphine (TOP, 90%), trioctylphosphine oxide (TOPO, 90%), starting materials for the production of CdTe quantum dots, Hexadecylamine (HDA, 98%), and anhydrous toluene were purchased from Aldrich. All reagents were used without further purification.

The experimental setup for the MBSL consists of a cylindrical quartz cell with a 5 mm diameter titanium horn (Misonix XL2020, USA) inserted. The system operates at an applied voltage of 220 W at 20 kHz. The temperature of the solution inside the cell is maintained at about 60 ° C by using a circulation bath in which the cell is immersed. MBSL conditions were fixed by adjusting the ultrasonic intensity, solvent temperature, and distance between the tip of the horn and the bottom of the cell.

CdCl ₂ (0.093 g, 0.5 mmol), Te powder (0.064 g, 0.5 mmol), HDA (0.5 g), TOP / TOPO (2.5 g, 2: 3 molar ratio) and 9 mL of toluene were added to the test cell without any thiol capping agent. It was political. The solution in the test cell was kept at 1.4 atm under argon atmosphere. For the preparation of CdTe quantum dots by size, ultrasound was irradiated for 5-40 minutes.

The final product was separated and purified by centrifugation at 4000 rpm for 20 minutes, and the precipitates which were supposed to be by-products such as cadmium chloride, tellurium and alkylammonium chloride salts were discarded. The dispersed quantum dots were precipitated with ethanol and the supernatant was discarded. The precipitated quantum dots were dried in vacuo for the preparation of TEM and XRD samples.

Example 2 Preparation of CdTe Quantum Dots in Octadecene Solvent

CdTe quantum dots were prepared in a manner similar to that of Example 1, except that octadecene was used instead of toluene as a solvent.

(Characterization)

Characterization of the CdTe quantum dot described below shows the results of using the CdTe quantum dot prepared according to Example 1 except for the XRD data.

XRD data were obtained by scanning Scintag XDS 2000 (Cu Kα = 1.54056 Hz) for 50 minutes at 0.02 ° step size at 0.02 ° / sec scan rate.

TEM images were obtained on a carbon coated 200 mesh copper TEM grid using a FEI tecnai G2 F30 with an acceleration voltage of 200 kV.

UV-vis absorbance and photoluminescence spectra were collected using a Uv-vis spectrometer (Scinco, S-3100) and a fluorescence spectrometer (Scinco, FS-2).

1 shows a typical XRD pattern (a) of a CdTe quantum dot prepared using toluene as a solvent and an XRD pattern (b) of a CdTe quantum dot prepared using octadecene as a solvent, both (111) and (220) There are three broad peaks corresponding to, and (311) planes. This is almost consistent with the previously reported CdTe peak (JCPDS card no. 15-0770). The crystal size of the quantum dots, calculated according to Scherrer's equation based on the XRD spectrum, is about 10 nm in diameter.

As shown in the electron diffraction pattern of FIG. 2, they are present in the cubic phase without any impurities such as cadmium oxide or tellurium and their crystalline phases. This result is quite interesting. This is because CdCl ₂ or Cd (OH) ₂ , NaBH ₄ and Te in water contain CdO and a large amount of unreacted Te as impurities when sonicated at the same ultrasonic voltage during the reaction time. To remove unreacted Te, the final product must be heat treated for several hours at a temperature of 600 ° C. or higher under vacuum. In addition, the average size of the CdTe particles produced in the aqueous solution process is about 30 to 50 nm in diameter, the particle size is not controlled.

The TEM image of FIG. 3 shows an appropriate size distribution of quantum dots with an average size of about 7-8 nm. Through this distribution, the growth of particles occurs uniformly, and the final product does not require a separate size selection process. Similarly, various CdTe quantum dots are readily produced in various colors by the simple ultrasonic chemistry described above; At the beginning of each experiment, during the initial sonication time for 2 minutes, the Te slurry was completely dissolved in the solvent and the color of the solution turned pale green, but no photoluminescence (PL) peaks appeared. This suggests that no CdTe is prepared in solution at this stage. Then, after additional sonication for 3 to 18 minutes, that is, when the total sonication time is increased from 5 to 20 minutes, quantum dots begin to form, and the color of the solution changes from pale green to yellow, followed by deep red. Change. After the sonication is finished, no color change of each solution is observed. This suggests that the growth of CdTe particles is over.

Figure 4 shows a photograph of the colloidal CdTe quantum solution prepared above, the normal UV-vis absorption spectrum, and the corresponding photo luminescence (PL) spectrum.

As shown in Fig. 4 (a) and (b), the color change of the solution from the initial pale green to yellow and deep red color is believed to result from increased crystal growth of CdTe quantum dots with increasing sonication time. . In the UV-vis spectrum, 508, 515, 540, 553, 568, and 576 nm peaks were observed during sonication times of 5, 7, 9, 12, 15, and 20 minutes, respectively. This result is very similar to the reported results. This is due to the chain red shift of the absorbance peak from the CdTe quantum dots as crystal growth increases.

4 (c) and (d) show PL peak (excitation wavelength: 400 nm) positions 529, 547, 578, 601, 614, and 631 nm at reaction times of 5, 7, 9, 12, 15 and 20 minutes. Similarity. The sonication reaction time for the synthesis of CdTe quantum dots is very fast and easy compared to existing solution based methods for the production of CdTe quantum dots.

The red shift and the PL peak of the magnitude dependent absorbance are explained by the relatively weaker quantum confinement effect. The size of these prepared CdTe quantum dots for 5-20 min sonication time is thought to be approximately 2-4 nm in diameter because their UV-vis and PL spectra are very similar to the results reported by Wuister et al.

After CdTe quantum dots were precipitated with ethanol and centrifuged, the precipitate was dried under vacuum for 30 minutes. The dark brown CdTe quantum dot powder was calcined at 400 ° C. for 1 hour under vacuum.

5 shows the XRD pattern (a), TEM image (b), and band gap energy (c) of the nanoparticles. It is noted that their crystal phases are still cubic and have strong sharp peaks characteristic at 23.7 °, 39.3 ° and 46.4 ° corresponding to the (111), (220) and (311) planes. In the TEM image of FIG. 5 (b), the particle size is about 8 to 30 nm, indicating that the particles grow irregularly by solid phase reactions between adjacent particles.

As shown in FIG. 5 (c), the band gap of calcined CdTe nanoparticles based on UV-vis spectral data was about 1.53 eV compared to 1.44 eV of bulk CdTe. This result is quite interesting because the bandgap that best matches solar cells is 1.5 eV.

In conclusion, various colloidal CdTe quantum dots in the range of about 2 to 10 nm were successfully synthesized using simple sonochemical reactions. It was found that their average size can be adjusted by adjusting the reaction conditions, and the CdTe particles have a constant morphology.

The crystal structure of the final product is the cubic phase and no other impurities are detected in the CdTe quantum dot manufacturing process. The color of the CdTe quantum dots changes from pale green to yellow and then deep red because of the varying sizes due to the sonication time.

In addition, CdTe nanoparticles were prepared by firing of CdTe quantum dots precipitated for 1 hour at 400 ° C., present in cubic phase, and their band gap was about 1.53 eV.

Claims (15)

Preparing a mixed solution of CdCl ₂ , Te or Se powder, surfactant and dispersant in a polar or nonpolar solvent; And
CdTe or by sonicating the mixed solution under multi-bubble sonoluminescence conditions using a frequency of 10 to 100 kHz and a power of 100 to 500 W while maintaining a temperature of 40 to 100 ° C. in an argon atmosphere. Preparing CdSe quantum dots or calcining the CdTe or CdSe quantum dots to convert them to CdTe or CdSe nanoparticles, respectively,
The solvent is at least one selected from the group consisting of a saturated hydrocarbon-based solvent, an unsaturated hydrocarbon-based solvent, an aromatic hydrocarbon-based solvent, and an aprotic polar solvent,
The surfactant is at least one selected from the group consisting of 1-hexadecylamine, octadecylamine and 4- (2-aminoethyl) phenol {4- (2-aminoethyl) phenol},
The dispersing agent is at least one selected from the group consisting of alkyl phosphine-based and alkyl phosphite-based compound group II to VI semiconductor quantum dot or nanoparticle manufacturing method.
delete delete delete delete delete The method of claim 1,
Sonication is carried out for 5 to 40 minutes.
delete The method of claim 1,
The semiconductor quantum dots have a diameter of 2 to 10 nm.
delete The method of claim 1,
Firing is carried out under vacuum at 300 to 600 ° C. for 1 to 3 hours.
The method of claim 1,
The nanoparticles have a diameter of 12 nm to 10 μm.
In the preparation of group II to VI semiconductor quantum dots or nanoparticles by sonication under multi-bubble sonoluminescence conditions,
Controlling the size of the CdTe or CdSe quantum dots by controlling the size of the CdTe or CdSe quantum dots or controlling the firing conditions to control the size of the CdTe or CdSe nanoparticles.
The method of claim 13,
The sonication time is 5 to 40 minutes.
The method of claim 13,
The firing conditions are carried out under vacuum at 300 to 600 ° C. for 1 to 3 hours.

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