Synthesis of quantum dot/polymer/layered-structure ceramic composite

Abstract

The present invention relates to a quantum dot and a preparation method therefor, and more specifically, to a novel quantum dot composite having high surface stability, and a preparation method therefor. The quantum dot composite according to the present invention constitutes a layered-structure ceramic composite in which the layered-structure ceramic comprises a polymer-quantum dot composite between the layers thereof.

Claims

1. A layered ceramic composite, configured such that a layered ceramic includes a polymer-quantum dot composite between layers thereof, wherein the polymer-quantum dot composite is a composite that comprises anionic polymers having a hydrophobic portion attach to organic molecules on the surface of the quantum dot.

2. The layered ceramic composite of claim 1, wherein the anionic polymer includes at least one anionic group selected from the group consisting of carboxylate, sulfate, sulfonate, nitrate, phosphate, and phosphonate.

3. The layered ceramic composite of claim 1, wherein the polymer is poly(maleic anhydride-alt-1-octadecene).

4. The layered ceramic composite of claim 1, wherein the layered ceramic is a layered double hydroxide.

5. The layered ceramic composite of claim 4, wherein the layered double hydroxide is represented by Formula (1) below:
[M.sub.m.sup.2+M.sub.n.sup.3+(OH).sub.2m+2n]X.sub.n/z.sup.z−.bH.sub.2O   (1) wherein M.sup.2+ is Zn.sup.2+, Mn.sup.2+, Ni.sup.2+, Co.sup.2+, Fe.sup.2+, Cu.sup.2+, Sn.sup.2+, Ba.sup.2+, Ca.sup.2+, or Mg.sup.2+; M.sup.3+ is Al.sup.3+, Cr.sup.3+, Fe.sup.3+, Co.sup.3+, Mn.sup.3+, Ni.sup.3+, Ce.sup.3+, or Ga.sup.3+; m and n are set so that m/n is 1˜10; b is 0˜10; and X is an anion selected from the group consisting of hydroxide, carbonate, bicarbonate, nitrate, chloride, bromide, sulfonate, sulfate, bisulfate, vanadate, tungstate, borate, phosphate, and Keggin-ions.

6. The layered ceramic composite of claim 1, wherein the quantum dot is a nanoparticle comprising at least one semiconductor material selected from the group consisting of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, InP, InAs, InSb, AlP, AlS, AlAs, AlSb, GaN, GaP, GaAs, GaSb, PbS, PbSe, Si, Ge, MgS, MgSe, and MgTe.

7. An illuminator, a display, an optical coating material, an anionic exchange material, a catalyst support, an electronic material, a UV absorbent, or a photocatalyst, comprising the layered ceramic composite of claim 1.

8. A method of manufacturing a layered ceramic composite, comprising reacting an anionic polymer-quantum dot composite with a cationic exfoliated layered double hydroxide, wherein the polymer-quantum dot composite is a composite that comprises anionic polymers having a hydrophobic portion attach to organic molecules on the surface of the quantum dot.

9. The method of claim 8, wherein the anionic polymer-quantum dot composite is configured such that a surface of quantum dots is surrounded by an anionic polymer.

10. The method of claim 8, wherein the exfoliated layered double hydroxide is mixed and reacted with an aqueous solution of the anionic polymer-quantum dot composite.

11. The method of claim 8, wherein the anionic polymer-quantum dot composite is obtained by mixing quantum dots dispersed in an organic solvent with an anionic polymer aqueous solution and then removing the organic solvent.

12. The method of claim 11, wherein the anionic polymer is an amphiphilic polymer comprising an anionic group reacting with the cationic exfoliated layered double hydroxide and a hydrophobic group linked to the quantum dots.

13. The method of claim 8, wherein the anionic polymer includes at least one anion selected from the group consisting of carboxylate, sulfate, sulfonate, nitrate, phosphate, and phosphonate.

14. The method of claim 8, wherein the anionic polymer is prepared by hydrolyzing poly(maleic anhydride-alt-1-octadecene).

15. The method of claim 8, wherein the exfoliated layered double hydroxide is obtained by substituting an interlayer ion of a layered double hydroxide.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 schematically illustrates a layered ceramic (layered double hydroxide) comprising positively charged 2D metal hydroxide layers and negatively charged molecules;

(2) FIG. 2 schematically illustrates formation of a quantum dot-polymer structure.

(3) FIG. 3 schematically illustrates formation of a quantum dot-polymer-layered ceramic composite through electrostatic self-assembly;

(4) FIG. 4 illustrates absorption and fluorescence spectra of CdSe/CdS/ZnS nanoparticles;

(5) FIG. 5 is a graph illustrating zeta potential distribution of the synthesized quantum dot-polymer structure;

(6) FIG. 6 is a graph illustrating hydrodynamic diameter distribution of the synthesized quantum dot-polymer structure;

(7) FIG. 7 is a graph illustrating X-ray diffraction analysis before and after Cl.sup.− substitution;

(8) FIG. 8 is a graph illustrating X-ray diffraction analysis of the layered double hydroxide before exfoliation (a) and after exfoliation (b);

(9) FIG. 9 illustrates fluorescence spectra of a quantum dot-polymer solution and a quantum dot-polymer-layered ceramic composite solution;

(10) FIG. 10 illustrates (a) images and (b) fluorescence images upon UV irradiation of the quantum dot-polymer solution and the quantum dot-polymer-layered ceramic composite solution after centrifugation;

(11) FIG. 11 illustrates (a) images and (b) fluorescence images upon UV irradiation of a quantum dot-polymer film and a quantum dot-polymer-layered ceramic composite film; and

(12) FIG. 12 illustrates fluorescence spectra of the quantum dot-polymer film and the quantum dot-polymer-layered ceramic composite film.

BEST MODE

(13) Hereinafter, a detailed description will be given of the present invention through the following examples, which are merely illustrate but are not construed as limiting the scope of the present invention. Also, it is noted that the scope of the present invention be defined by the claims by those skilled in the art.

EXAMPLE 1

Synthesis of Quantum Dots, Introduction of Surface Thereof with Polymer, and Transfer Thereof to Aqueous Solution

(14) CdSe/CdS/ZnS was prepared as follows. Octadecene and oleylamine were placed in a round-bottom flask and heated to 100° C. While a vacuum state and a nitrogen injection state were alternately changed, the ambient atmosphere was consequently fully filled with nitrogen gas. Thereafter, the temperature of the round-bottom flask was increased to 300° C., and solutions of cadmium (Cd) in octadecene and selenium (Se) in octadecene were simultaneously placed in the high-temperature flask at a ratio of Cd to Se of 1:5. As such, the ratio of Cd to Se may be adjusted depending on the desired nanoparticle size. The flask reactor was slowly cooled, thus obtaining CdSe nanoparticles dispersed in the organic solvent. The obtained CdSe nanoparticles were dispersed in the flask containing octadecene and oleylamine, and heated to 100° C. While a vacuum state and a nitrogen injection state were alternately changed, the ambient atmosphere was consequently fully filled with nitrogen gas. Then, the temperature of the flask was increased to 240° C., and reaction was carried out for 10 min each while alternately adding solutions of Cd-oleate in octadecene and sulfur (S) in octadecene. These procedures were repeated three times. Also, reaction using solutions of Zn-oleate in octadecene and S in octadecene was repeated three times in the same manner as above. The reaction temperature was further maintained for about 1 hr, and the flask reactor was slowly cooled to room temperature, giving CdSe/CdS/ZnS nanoparticles dispersed in the organic solvent. The CdSe/CdS/ZnS nanoparticles have absorption and fluorescence properties as illustrated in FIG. 4.

(15) In 2 mL of distilled water, 100 nmol poly(maleic anhydride-alt-1-octadecene), and 1 nmol quantum dots dispersed in the organic solvent were placed and then sonicated for 20 min. While the mixture was stirred, it was heated to 80° C. and the organic solvent was selectively evaporated, thus obtaining a quantum dot-polymer structure dispersed in the aqueous solution. The absorption zeta potential is used for analysis of the kind of surface charge of colloidal particles and the size thereof. The zeta potential of the quantum dot-polymer structure is −29.4±3.17 mV (FIG. 5), and the hydrodynamic diameter thereof approximates to 54.5±10.5 nm (FIG. 6).

EXAMPLE 2

Synthesis and Exfoliation of Layered Ceramic (e.g. Layered Double Hydroxide)

(16) At room temperature, 0.01 M zinc nitrate and 0.003 M aluminum nitrate aqueous solutions were added with 0.35 M ammonia with stirring. While the resulting mixture was stirred for 24 hr, the reaction temperature was maintained at room temperature. After completion of the reaction, the layered double hydroxide composite was precipitated using a centrifuge, and the supernatant was then discarded, followed by drying in air. 0.2 g of a layered double hydroxide powder containing CO.sub.3.sup.2− as a negatively charged material was added to a 1 M NaCl-HCl solution, and then stirred for 12 hr in a nitrogen atmosphere. The layered double hydroxide composite was precipitated using a centrifuge, and the supernatant was then discarded, followed by drying in air. Through the NaCl-HCl reaction, CO.sub.3.sup.2− was substituted with Cl.sup.−. As is apparent from the results of X-ray diffraction analysis of FIGS. 7, (003) and (006) peaks of the layered double hydroxide are shifted toward a small angle compared to before substitution, from which CO.sub.3.sup.2− can be confirmed to be substituted with Cr.

(17) The layered double hydroxide where the negatively charged molecules between the sheets had been substituted with Cl− was placed in a formamide solution in a nitrogen atmosphere, and stirred for 48 hr, thereby exfoliating the layered double hydroxide.

(18) As illustrated in FIG. 8, the size of (003) peak that shows the 2D metal hydroxide layer stack is relatively small compared to before the reaction, from which exfoliation can be confirmed to occur.

EXAMPLE 3

Synthesis of Quantum Dot-Polymer-Layered Ceramic Composite

(19) The formamide solution containing the exfoliated layered double hydroxide was separated into the formamide supernatant and the layered double hydroxide precipitate using a centrifuge. The supernatant was discarded, and the precipitate was added with an aqueous solution containing the quantum dot-polymer structure and then stirred at room temperature for 1 hr. As illustrated in FIG. 9, the composite having fluorescence is formed and the intensity of fluorescence is equal to or greater than the intensity before formation of the composite, and the position or shape of the peak can be seen to be maintained.

(20) Upon centrifugation at 2000 rpm for 3 min using a centrifuge, as illustrated in FIG. 10, while the composite is formed, the quantum dot-polymer structure is trapped in the layered ceramic and thus precipitated. The quantum dot-polymer structure centrifuged under the same conditions is well dispersed in the aqueous solution, with no precipitate.

EXAMPLE 4

Formation of Film Via Drop Casting and Fluorescence Properties

(21) The quantum dot-polymer-layered ceramic composite solution was dropped on a glass substrate and the solvent was evaporated at room temperature, thus forming a composite film. As illustrated in FIG. 11, the quantum dot-polymer-layered ceramic composite film is relatively uniform compared to the quantum dot-polymer structure film under the condition that the quantum dots have the same concentration. Although such a composite film contains the quantum dots in the same concentration, it exhibits relatively strong fluorescence properties (FIG. 12).