Method for preparing nanoparticles using carbene derivatives

This non-provisional application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2008-0046735, filed on May 20, 2008 in the Korean Intellectual Property Office (KIPO), the entire contents of which are incorporated herein by reference.

1. Field

This disclosure is directed to a method for preparing nanoparticles using carbene derivatives.

2. Description of the Related Art

Nanoparticles (also called “quantum dots”) are defined as crystalline materials having a size of a few nanometers, and consist of several hundred to several thousand atoms. Since such small-sized nanoparticles have a large surface area per unit volume, most of the constituent atoms of the nanoparticles are present on the surface of the nanoparticles. Based on this characteristic structure, nanoparticles exhibit quantum confinement effects and shows electrical, magnetic, optical, chemical and mechanical properties different from those inherent to the constituent atoms of the nanoparticles. Accordingly, semiconductor crystalline nanoparticles have attracted much attention, because they can be applied to various devices, based on novel photoelectric properties such as the ability to control energy bandgaps through variation in size.

Vapor deposition processes, including metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE), have been used to prepare nanoparticles. Further, a wet chemistry technique wherein a precursor material is added to an organic solvent to grow nanoparticles has made remarkable progress. According to the wet chemistry technique, as a crystal is grown, a surfanctant is coordinated to the surface of the nanocrystal to control the crystal growth. Accordingly, the wet chemistry technique has an advantage in that the size, shape and uniformity of nanocrystals can be controlled in a relatively simple manner at low cost, compared to conventional vapor deposition processes, e.g., MOCVD and MBE (molecular beam epitaxy).

The characteristics of precursors used are known to be one factor required for controlling the size, shape, structure and uniformity of nanoparticles which are synthesized by controlling reaction mechanism or reaction rate. Precursors used to efficiently synthesize nanoparticles are limited to several types of materials.

Accordingly, research has been made on precursors capable of more efficiently controlling the size, shape, structure and uniformity of nanoparticles upon synthesis of the nanoparticles.

Therefore, exemplary embodiments provide a method for preparing nanoparticles using precursors that can more efficiently control the size, shape, structure and uniformity of the nanoparticles.

Other exemplary embodiments provide nanoparticles having a uniform size, shape and structure.

Disclosed herein is a method for preparing nanoparticles including adding one or more precursors with one or more metal precursors to an organic solvent to grow a crystal, wherein carbene derivatives represented by the following Formula 1 or 2 is used as one of the precursor:

wherein X is O, S, Se, Te or Po;

R 1 and R 2 are each independently substituted or unsubstituted C 5 -C 50 aryl, or substituted or unsubstituted C 1 -C 50 alkyl; and

substituents of R 1 and R 2 , which are identical to or different from each other, are each independently C 1 -C 20 alkyl, C 3 -C 20 cycloalkyl, C 5 -C 30 heterocycloalkyl, C 2 -C 20 alkenyl, C 6 -C 20 aryl, C 5 -C 30 heteroaryl, C 7 -C 20 arylalkyl, C 7 -C 30 heteroarylalkyl or carbonyl,

wherein X is O, S, Se, Te or Po;

R 3 and R 4 are each independently substituted or unsubstituted C 5 -C 50 aryl, or substituted or unsubstituted C 1 -C 50 alkyl; and

substituents of R 3 and R 4 , which are identical to or different from each other, are each independently C 1 -C 20 alkyl, C 3 -C 20 cycloalkyl, C 5 -C 30 heterocycloalkyl, C 2 -C 20 alkenyl, C 6 -C 20 aryl, C 5 -C 30 heteroaryl, C 7 -C 20 arylalkyl, C 7 -C 30 heteroarylalkyl or carbonyl.

Further disclosed herein are nanoparticles prepared by the method.

The nanoparticles are selected from the group consisting of Group XII-XVI compounds, Group XIII-XVI compounds, Group XIV-XVI compounds and mixtures thereof. More specifically, the nanoparticles are selected from the group consisting of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, PbS, PbSe, PbTe, AlS, AlSe, AlTe, GaS, GaSe, GaTe, InS, InSe, InTe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbS, PbSe, PbTe and mixtures thereof.

The nanoparticles have a diameter of 3 to 50 nm, may be doped with a hetero-metal element and may have a core-shell or multi-layer structure.

Exemplary embodiments will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. FIGS. 1-15 represent non-limiting, exemplary embodiments as described herein.

FIG. 1 is NMR spectra of the carbene precursor prepared in Preparation Example 1;

FIG. 2 is a transmission electron micrograph (TEM) of nanoparticles obtained in Example 1;

FIG. 3 is a transmission electron micrograph (TEM) of nanoparticles obtained in Example 2;

FIG. 4 is a transmission electron micrograph (TEM) of nanoparticles obtained in Example 3;

FIG. 5 is a transmission electron micrograph (TEM) of nanoparticles obtained in Example 4;

FIG. 6 is a transmission electron micrograph (TEM) of the nanoparticle obtained in Example 5;

FIG. 7 is a transmission electron micrograph (TEM) of nanoparticles obtained in Example 6;

FIG. 8 is a transmission electron micrograph (TEM) of nanoparticles obtained in Example 7;

FIG. 9 is a transmission electron micrograph (TEM) of nanoparticles obtained in Example 8;

FIGS. 10A to 10C are graphs showing results of energy dispersive X-ray spectroscopy (EDX) of nanoparticles obtained in Example 8;

FIG. 11 is UV absorption spectra of nanoparticles obtained in Examples 9 and 10;

FIG. 12 is photoluminescence spectra of nanoparticles obtained in Examples 9 and 10;

FIG. 13 is photoluminescence spectra of nanoparticles obtained in Example 11 and Comparative Example 1;

FIG. 14 is a transmission electron micrograph (TEM) of nanoparticles obtained in Comparative Example 1; and

FIGS. 15A to 15C are graphs showing the results of energy dispersive X-ray spectroscopy (EDX) of nanoparticles obtained in Comparative Example 2.

Hereinafter, a detailed description will be given of exemplary embodiments with reference to the accompanying drawings.

It will be understood that when an element or layer is referred to as being “on,” “interposed,” “disposed,” or “between” another element or layer, it can be directly on, interposed, disposed, or between the other element or layer or intervening elements or layers may be present.

It will be understood that, although the terms first, second, third, and the like may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, first element, component, region, layer or section discussed below could be termed second element, component, region, layer or section without departing from the teachings of the present invention.

As used herein, the singular forms “a,” “an” and “the” are intended to comprise the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. In the drawings, the thickness of layers and regions are exaggerated for clarity.

According to exemplary embodiments, provided is a method for preparing nanoparticles including adding one or more precursors with one or more metal precursors to an organic solvent to grow a crystal, wherein carbene derivatives represented by the following Formula 1 or 2 are used as one of the precursor:

wherein X is O, S, Se, Te or Po;

R 1 and R 2 are each independently substituted or unsubstituted C 5 -C 50 aryl, or substituted or unsubstituted C 1 -C 50 alkyl; and

substituents of R 1 and R 2 , which are identical to or different from each other, are each independently C 1 -C 20 alkyl, C 3 -C 20 cycloalkyl, C 5 -C 30 heterocycloalkyl, C 2 -C 20 alkenyl, C 6 -C 20 aryl, C 5 -C 30 heteroaryl, C 7 -C 20 arylalkyl, C 7 -C 30 heteroarylalkyl or carbonyl,

wherein X is O, S, Se, Te or Po;

R 3 and R 4 are each independently substituted or unsubstituted C 5 -C 50 aryl, or substituted or unsubstituted C 1 -C 50 alkyl; and

substituents of R 3 and R 4 , which are identical to or different from each other, are each independently C 1 -C 20 alkyl, C 3 -C 20 cycloalkyl, C 5 -C 30 heterocycloalkyl, C 2 -C 20 alkenyl, C 6 -C 20 aryl, C 5 -C 30 heteroaryl, C 7 -C 20 arylalkyl, C 7 -C 30 heteroarylalkyl or carbonyl.

The carbene derivatives according to exemplary embodiments may have one or more substituents. The substituents may be identical to or different from each other, and specific examples thereof include, but are not limited to, C 1 -C 20 alkyl, C 3 -C 20 cycloalkyl, C 5 -C 30 heterocycloalkyl, C 2 -C 20 alkenyl, C 6 -C 20 aryl, C 5 -C 30 heteroaryl, C 7 -C 20 arylalkyl, and C 7 -C 30 heteroarylalkyl.

The alkyl may be straight-chained or branched, and specific examples thereof include methyl, ethyl, propyl, isobutyl, sec-butyl, tert-butyl, pentyl, iso-amyl and hexyl.

The term “cycloalkyl” as used herein refers to a C 3 -C 20 monovalent monocyclic system. At least one hydrogen atom contained in the cycloalkyl group may be substituted.

The term “heterocycloalkyl” as used herein refers to a C 5 -C 30 monovalent monocyclic system consisting of one, two or three heteroatoms selected from N, O, P and S atoms and the remaining ring carbon atoms. At least one hydrogen atom contained in the heterocycloalkyl group may be substituted.

Specific examples of the alkenyl include vinyl, allyl, propenyl, butenyl, hexenyl and cyclohexenyl.

The term “aryl” as used herein refers to a carbocyclic aromatic system including one or more aromatic rings in which the rings may be attached together in a pendent manner or may be fused. Specific examples of the aryl group include aromatic groups, such as phenyl, naphthyl, and tetrahydronaphthyl. At least one hydrogen atom contained in the aryl group may be substituted.

The term “heteroaryl” as used herein refers to a C 5 -C 30 cyclic aromatic system consisting of one to three heteroatoms selected from N, Of P and S atoms and the remaining ring carbon atoms in which the rings may be attached together in a pendant manner or may be fused. At least one hydrogen atom contained in the heteroaryl group may be substituted.

The term “arylalkyl” as used herein refers to a group in which a part of hydrogen atoms contained in the aryl group defined above are substituted with lower alkyl radicals, such as methyl, ethyl and propyl. Examples of the arylalkyl group include benzyl and phenylethyl. At least one hydrogen atom contained in the arylalkyl group may be substituted.

The term “heteroarylalkyl” as used herein refers to a group in which a part of hydrogen atoms contained in the heteroaryl group defined above are substituted with lower alkyl radicals. At least one hydrogen atom included in the heteroarylalkyl group may be substituted with the same substituent as defined with respect to the “alkyl group”. When the carbene derivatives have a steric barrier based on a long-chain alkyl group, it is more stable. R 1 , R 2 , R 3 and R 4 may be each independently C 5 -C 30 aryl, or C 1 -C 30 alkyl; and more C 5 -C 18 aryl, or C 1 -C 18 alkyl. Carbene derivatives with C 6 -C 18 alkyl group may be used as precursor.

The carbene derivatives of Formula 1 or 2 according to exemplary embodiments may be represented by Formulae 3 to 26 below:

The carbene derivatives represented by Formula 1 or 2 have a strong bond between the Group XVI element and carbene. Accordingly, when the derivatives are used as a Group XVI element precursor in the nanoparticle wet synthesis process, it can retard the release rate of the Group XVI element, thus more favorably controlling the reaction rate. When trialkylsilyl or trialkylphosphine compounds, conventional Group XVI element precursors, are used, Group XVI elements are significantly rapidly released and nanoparticles having a size not less than a predetermined level are grown in a specific direction without maintaining their spherical shape. On the other hand, the use of the carbene derivatives according to the exemplary embodiments enables production of nanoparticles having a uniform size, shape and structure.

In the method for preparing nanoparticles according to exemplary embodiments, a reaction mixture is heated for a specific time to synthesize nanoparticles. Alternatively, the synthesis of the nanoparticles may be carried out by first preparing a primary reaction mixture containing the carbene compound, and after heating the primary reaction mixture, adding metal precursors thereto at a high temperature.

According to exemplary embodiments, the method for preparing nanoparticles may comprise i) mixing metal precursors, carbene derivatives of Formula 1 or 2 and an organic solvent with one another to prepare a reaction mixture; and ii) heating the reaction mixture.

In step ii), the heating temperature may be about 250° C. to about 320° C. When the heating temperature is about 300° C., spherical nanoparticles can be more efficiently obtained. The reaction mixture may further comprise a surfactant.

According to other embodiments, a method for preparing nanoparticles may comprise i) mixing the carbene derivatives of Formula 1 or 2 with an organic solvent to prepare a primary reaction mixture; and ii) hot-injecting metal precursors to the heated primary reaction mixture, followed by mixing. In step i), the heating temperature is preferably about 250° C. to about 320° C. In step ii), the metal precursors are sequentially hot-injected to the heated primary reaction mixture at the same temperature as the heating temperature of the primary reaction mixture, and after hot-injection, the temperature of the reaction mixture may maintained or elevated. At this time, the temperature is preferably maintained in the range of about 250° C. to about 320° C. The reaction time of step ii) is not particularly limited, but may be about 5 to about 72 hours, more about 30 minutes to about 24 hours, and more about 1 hour to 2 hours are good. The metal precursors may be added together with a surfactant.

In the method for preparing nanoparticles, a reaction mixture additionally containing a dopant is used in the reaction, thereby preparing doped nanoparticles. Examples of dopants that can be used in the method include, but are not limited to: transition metals selected from scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu) and zinc (Zn); precious metals selected from gold (Au), silver (Ag), platinum (Pt) and iridium (Ir); alkali metals selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr); and mixtures thereof.

When doped nanoparticles are prepared according to exemplary embodiments, the release rate of the Group XVI element can be retarded, as compared to conventional metal precursors, due to the strong bond between the Group XVI element and the carbene compound, thus enabling the nanoparticles to be uniformly doped with the dopant.

Examples of metal precursors that can be used to provide an element other than the Group XVI element in the preparing method of nanoparticles include, but are not limited to, dimethyl zinc, diethyl zinc, zinc acetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinc chloride, zinc fluoride, zinc carbonate, zinc cyanide, zinc nitrate, zinc oxide, zinc peroxide, zinc perchlorate, zinc sulfate, dimethyl cadmium, diethyl cadmium, cadmium acetate, cadmium acetylacetonate, cadmium iodide, cadmium bromide, cadmium chloride, cadmium fluoride, cadmium carbonate, cadmium nitrate, cadmium oxide, cadmium perchlorate, cadmium phosphide, cadmium sulfate, mercury acetate, mercury iodide, mercury bromide, mercury chloride, mercury fluoride, mercury cyanide, mercury nitrate, mercury oxide, mercury perchlorate, mercury sulfate, lead acetate, lead bromide, lead chloride, lead fluoride, lead oxide, lead perchlorate, lead nitrate, lead sulfate, lead carbonate, tin acetate, tin bisacetylacetonate, tin bromide, tin chloride, tin fluoride, tin oxide, tin sulfate, germanium tetrachloride, germanium oxide, germanium ethoxide, gallium acetylacetonate, gallium chloride, gallium fluoride, gallium oxide, gallium nitrate, gallium sulfate, indium chloride, indium oxide, indium acetate, indium nitrate, and indium sulfate.

In the preparing method of nanoparticles according to exemplary embodiments, an organic solvent or a surfactant may be used for the reaction mixture. This material enables easy dispersion, thus yielding uniform nanoparticles. The organic solvent that can be used for the method according to exemplary embodiments is selected from the group consisting of, but not limited to: C 6-24 primary alkyl amines, C 6-24 secondary alkyl amines and C 6-24 tertiary alkyl amines; C 6-24 primary alcohols, C 6-24 secondary alcohols and C 6-24 tertiary alcohols; C 6-24 ketones and C 6-24 esters; C 6-24 heterocyclic compounds containing 1-3 nitrogen or sulfur; C 6-24 alkanes, C 6-24 alkenes and C 6-24 alkynes; and trioctylamine, trioctylphosphine and trioctylphosphine oxide.

Examples of surfactants that can be used for the method according to exemplary embodiments include C 6 -C 24 alkanes and alkenes having a terminal carboxyl (COOH) group; C 6 -C 24 alkanes and alkenes having a terminal phosphoryl (POOH) group; C 6 -C 24 alkanes and alkenes having a terminal sulfinic acid (SOOH) group; and C 6 -C 24 alkanes and alkenes having a terminal amino (NH 2 ) group.

Specific examples of surfactants include, but are not limited to, oleic acid, stearic acid, palmitic acid, hexylphosphonic acid, n-octylphosphonic acid, tetradecylphosphonic acid, octadecylphosphonic acid, n-octyl amine and hexadecyl amine.

The method for preparing nanoparticles may be used to prepare nanoparticles having a multi-layer structure comprising two or more layers. At this time, the preparing method of nanoparticles may be used for the formation of one or more layers. For example, in the case of core-shell structure nanoparticles, core or shell nanoparticles can be formed using the method according to exemplary embodiments. In the case of tri-layer structure nanoparticles, an intermediate layer or the outermost layer may be formed using the method. In particular, in order to form the intermediate layer of multi-layer structure nanoparticles, reactivity must be retarded. Accordingly, nanoparticles can be efficiently prepared using the method of exemplary embodiments.

According to other exemplary embodiments, provided are nanoparticles prepared by the method.

The nanoparticles are selected from the group consisting of Group XII-XVI compounds, Group XIII-XVI compounds, Group XIV-XVI compounds and mixtures thereof. The nanoparticles may comprise CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, PbS, PbSe, PbTe, AlS, AlSe, AlTe, GaS, GaSe, GaTe, InS, InSe, InTe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbS, PbSe, PbTe and mixtures thereof.

Preferably, the nanoparticles may have a diameter of about 3 to about 50 nm and take a spherical shape, but the exemplary embodiments are not limited thereto. The nanoparticles may be doped with a hetero-metal element. In addition, the nanoparticles may be a core-shell structured nanocrystal consisting of a core and an over-coating that surrounds the core, or a core-containing multi-layer nanocrystal.

The exemplary embodiments will now be described in further detail with reference to the following examples. These examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Preparation Example 1

Synthesis of Se Carbene Precursor

Hexadecylmethylimidazolium iodide (3 g, 6.91 mmol) and potassium carbonate (K 2 CO 3 , 4.77 g, 34.51 mmol) were added to 50 mL of methanol and were then refluxed. Selenium (1.64 g, 20.72 mmol) was added thereto and refluxed at ambient temperature for about 12 hours. The remaining K 2 CO 3 and Se were removed using a glass filter, the methanol was removed using an evaporator, and then extracted with dichloromethane/sodium bicarbonate (NaHCO 3 ). The dichloromethane layer was dried over MgSO 4 and separated by column chromatography employing hexane/ether (4:1) as an eluent to yield 1-hexadecyl-3-methyl-4-imidazoline-2-selone. The NMR spectrum of this compound is shown in FIG. 1 .

1 H NMR (CDCl 3 , 300 MHz): δ 6.88 (brs, 2H), 4.10 (t, J=7.5 Hz, 2H), 3.71 (3H, s), 1.80 (q, J=7.2 Hz, 2H), 1.25 (m, 28H), 0.88 (t, J=6.9 Hz, 3H) ppm.