Nanoparticles passivated with cationic metal-chalcogenide compound

Abstract

Provided are nanoparticles passivated with a cationic metal-chalcogenide complex (MCC) and a method of preparing the same. A passivated nanoparticle includes: a core nanoparticle; and a cationic metal-chalcogenide compound (MCC) fixed on a surface of the core nanoparticle.

Claims

1. A passivated nanoparticle comprising: a core nanoparticle; and a cationic metal-chalcogenide which passivates the core nanoparticle, wherein the cationic metal-chalcogenide is fixed on a surface of the core nanoparticle, and wherein the cationic metal-chalcogenide is selected from the group consisting of Zn.sub.2S.sub.2, Zn—Se—Se—Zn, Zn.sub.2Te.sub.2, Cu.sub.2S.sub.2, Cu.sub.2Se.sub.2, Cu.sub.2Te.sub.2, Mn.sub.2S.sub.2, Mn.sub.2Se.sub.2, Mn.sub.2Te.sub.2, Fe.sub.2S.sub.2, Fe.sub.2Se.sub.2, Fe.sub.2Te.sub.2, Co.sub.2S.sub.2, Co.sub.2Se.sub.2, Co.sub.2Te.sub.2, and mixtures thereof.

2. The passivated nanoparticle of claim 1, wherein the core nanoparticle is a quantum dot, a metal nanocrystal (NC), a magnetic NC, an oxide NC, a nanowire, or a nanoplate.

3. The passivated nanoparticle of claim 2, wherein the quantum dot is selected from the group consisting of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, CdHgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, SnPbSTe, Si, Ge, SiC, SiGe, and combinations thereof.

4. The passivated nanoparticle of claim 2, wherein the quantum dot has a core-shell structure or a core-shell-shell structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and/or other aspects will become apparent and more readily appreciated from the following description of embodiments, taken in conjunction with the accompanying drawings in which:

(2) FIG. 1 is a schematic view illustrating a quantum dot passivated with a cationic metal-chalcogenide compound (MCC) (Zn.sub.2Se.sub.2) according to an embodiment;

(3) FIG. 2 illustrates the results of nuclear magnetic resonance (NMR) analysis of Na.sub.2Se.sub.2 formed during a process of preparing a cationic MCC according to an embodiment (77Se NMR, solvent: methanol);

(4) FIG. 3 illustrates the results of an NMR analysis of Zn.sub.2Se.sub.2(ClO.sub.4).sub.2 formed during the process of preparing a cationic MCC according to an embodiment (77Se NMR, solvent: dimethyl sulfoxide (DMSO));

(5) FIG. 4 illustrates the results of an NMR analysis of Na.sub.2Se.sub.2 formed during the process of preparing a cationic MCC according to an embodiment (77Se NMR, solvent: DMSO);

(6) FIG. 5 illustrates the results of fast atom bombardment-mass spectroscopy (FAB-MASS) analysis of Zn.sub.2Se.sub.2(ClO.sub.4).sub.2 formed during the process of preparing a cationic MCC according to an embodiment;

(7) FIG. 6 is a schematic view illustrating a process in which quantum dots (CdSe) in a first organic solvent (hexane) are transferred to a second organic solvent (DMSO) layer to be bonded with a cationic MCC, during a process of preparing passivated quantum dots according to an embodiment of the present invention;

(8) FIG. 7 illustrates the results of a surface zeta potential analysis of quantum dots (CdSe) substituted with Zn.sub.2Se.sub.2(ClO.sub.4).sub.2 according to an embodiment; and

(9) FIG. 8 shows the results of an ultraviolet (UV) absorption spectrum analysis of quantum dots (CdSe) substituted with Zn.sub.2Se.sub.2(ClO.sub.4).sub.2 according to an embodiment.

DETAILED DESCRIPTION

(10) Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments herein are described below, by referring to the figures, to explain aspects of the present disclosure.

(11) A metal-chalcogenide compound is provided according to an aspect of the present disclosure. Particular examples of the metal-chalcogenide compound may be Zn.sub.2S.sub.2, Zn.sub.2Se.sub.2, Zn.sub.2Te.sub.2, Cu.sub.2S.sub.2, Cu.sub.2Se.sub.2, Cu.sub.2Te.sub.2, Mn.sub.2S.sub.2, Mn.sub.2Se.sub.2, Mn.sub.2Te.sub.2, Fe.sub.2S.sub.2, Fe.sub.2Se.sub.2, Fe.sub.2Te.sub.2, Co.sub.2S.sub.2, Co.sub.2Se.sub.2, Co.sub.2Te.sub.2, or a mixture thereof. In the metal-chalcogenide compound, the metal atoms have a positive charge. For example, with respect to Zn.sub.2S.sub.2 having a Zn—S—S—Zn bond structure, one of the outer most electrons of zinc (Zn) is covalently bonded with sulfur (S), but the other electron is not bonded with S. Zn is a group 2 element that has an electron-donating property. Accordingly, in a solution, Zn loses the outermost electron that is not bonded with S. As a result, Zn in the Zn—S—S—Zn bond structure has a positive charge in the solution. According to such a mechanism or similar mechanism, the metal-chalcogenide compound ends up having cationicity in the solution. A zinc-chalcogenide compound may be used as a passivation agent for nanoparticles.

(12) A passivated nanoparticle provided according to another aspect of the present disclosure includes a core nanoparticle and a cationic metal-chalcogenide compound (MCC) fixed on a surface of the core nanoparticle.

(13) FIG. 1 is a schematic view illustrating a nanoparticle (here, a quantum dot) passivated with a cationic MCC (Zn.sub.2Se.sub.2) according to an embodiment. Referring to FIG. 1, Zn atoms in Zn.sub.2Se.sub.2 are bonded in cationic form to the surface of the quantum dot. Since the Zn atoms have positive charges, the Zn atoms may be bonded to an anionic component of the nanoparticle (e.g., to the selenium (Se) atoms in a CdSe quantum dot), or may be bonded in an orbital form.

(14) Examples of the cationic MCC include Zn.sub.2S.sub.2, Zn.sub.2Se.sub.2, Zn.sub.2Te.sub.2, Cu.sub.2S.sub.2, Cu.sub.2Se.sub.2, Cu.sub.2Te.sub.2, Mn.sub.2S.sub.2, Mn.sub.2Se.sub.2, Mn.sub.2Te.sub.2, Fe.sub.2S.sub.2, Fe.sub.2Se.sub.2, Fe.sub.2Te.sub.2, Co.sub.2S.sub.2, Co.sub.2Se.sub.2, Co.sub.2Te.sub.2, or combinations thereof.

(15) The core nanoparticle is not particularly limited, and, for example, may be any nanoparticle, such as a quantum dot, a metal nanocrystal (NC), a magnetic NC, an oxide NC, a nanowire, or a nanoplate. As an example, the core nanoparticle may have a particle size ranging from about 1 nm to about 99 nm.

(16) The quantum dot may, for example, be formed from a group II-VI semiconductor compound, a group III-V semiconductor compound, a group IV-VI semiconductor compound, a group IV element or compound, or a combination thereof.

(17) Particular examples of the quantum dot include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, CdHgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, SnPbSTe, Si, Ge, SiC, SiGe, or combinations thereof.

(18) The quantum dot may, for example, have a core-shell structure. In that case, the core and the shell each may be composed of a single layer or two or more layers. For example, the quantum dot may have a core-shell-shell structure, and particularly, may be composed of CdSe/CdS/ZnS. Other nanoparticles may also have a core-shell structure.

(19) According to another aspect of one or more exemplary embodiments, a passivated nanoparticle colloid including passivated nanoparticles according to an aspect of the present disclosure and a dispersion medium in which the passivated nanoparticles are dispersed is provided. The dispersion medium may include, for example, ethanol amine, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or formamide.

(20) The passivated nanoparticle colloid may be used as a thin film-forming material. For example, an appropriate amount of the colloid may be dispensed on a substrate and then the substrate may be coated using a method such as spin coating, and thus, a thin film containing passivated nanoparticles may be formed.

(21) A method of preparing a cationic MCC, according to another aspect herein, includes: reacting a chalcogen element with NaBH.sub.4 to form a sodium-chalcogenide compound; reacting the sodium-chalcogenide compound with metal perchlorate to form metal-chalcogenide perchlorate; and reacting the metal-chalcogenide perchlorate with ethanolamine to form an MCC.

(22) A point to be noted in the above method is that sodium chalcogenide, an intermediate product that is easily formed, is prepared in advance, and sodium atoms are then substituted with zinc atoms, and thus, zinc chalcogenide may be effectively formed.

(23) For example, S, Se, or tellurium (Te) may be used as a chalcogen element, and as a result, the zinc-chalcogenide compound thus formed may be Zn.sub.2S.sub.2, Zn.sub.2Se.sub.2, or Zn.sub.2Te.sub.2.

(24) In the reacting the chalcogen element with NaBH.sub.4 to form a sodium-chalcogenide compound, the reaction medium may be, for example, methanol, ethanol, butanol, or isopropanol; the reaction atmosphere may be, for example, an oxidation atmosphere or an inert atmosphere; and the reaction temperature may be, for example, in the range of from about 20° C. to about 200° C. In an embodiment using Se and NaBH.sub.4, the reaction formula for forming a sodium-chalcogenide compound (i.e., Na.sub.2Se.sub.2) is:
3Se+2NaBH.sub.4.fwdarw.Na.sub.2Se.sub.2+H.sub.2Se+2B(OC.sub.2H.sub.5).sub.3+6H.sub.2

(25) In the reacting of the sodium-chalcogenide compound with metal perchlorate to form metal-chalcogenide perchlorate, the reaction medium may be, for example, methanol, ethanol, butanol, or isopropanol; the reaction atmosphere may be, for example, an oxidation atmosphere or an inert atmosphere; and the reaction temperature may be, for example, in the range of from about 20° C. to about 200° C. Examples of the metal perchlorate include zinc perchlorate, tin perchlorate, indium perchlorate, antimony perchlorate, sodium perchlorate, silver perchlorate, iron perchlorate, potassium perchlorate, magnesium perchlorate, barium perchlorate, calcium perchlorate, cadmium perchlorate, aluminum perchlorate, manganese perchlorate, platinum perchlorate, or mixtures thereof.

(26) In an embodiment using Na.sub.2Se.sub.2 and Zn(ClO.sub.4).sub.2, the reaction formula for forming zinc-chalcogenide perchlorate (i.e., Zn.sub.2Se.sub.2(ClO.sub.4).sub.2) is:
Na.sub.2Se.sub.2+2Zn(ClO.sub.4).sub.2.fwdarw.Zn.sub.2Se.sub.2(ClO.sub.4).sub.2+2Na(ClO.sub.4).sub.2

(27) In the reacting of the metal-chalcogenide perchlorate with ethanolamine to form an MCC, the reaction medium may be, for example, ethanolamine, hydrazine, or hydrazine hydrate; the reaction atmosphere may be, for example, an oxidation atmosphere or an inert atmosphere; and the reaction temperature may be, for example, in the range of from about 20° C. to about 200° C. The MCC formed in this step may be in the form of a complex of ethanolamine and zinc-chalcogenide or may be in the form of a metal-chalcogenide coordinated with ethanolamine. Also, the MCC may be in the form of a complex of hydrazine or hydrazine hydrate and metal-chalcogenide or may be in the form of a metal-chalcogenide coordinated with hydrazine or hydrazine hydrate.

(28) A method of preparing passivated nanoparticles, according to another aspect herein, includes: providing a first dispersion, which is a dispersion of nanoparticles having a first organic ligand in a first organic solvent; preparing a second solution, which is a solution of a cationic MCC in a second organic solvent; mixing the first dispersion and the second solution to form a mixed solution; and stirring the mixed solution to exchange the first organic ligand of the nanoparticles with the cationic MCC.

(29) In the first dispersion, nanoparticles in the state of being coordinated with the first organic ligand are dispersed in the first organic solvent.

(30) Examples of the first organic ligand may include trioctylphosphine (TOP), trioctylphosphine oxide (TOPO), oleic acid, oleylamine, octylamine, trioctylamine, hexadecylamine, octanethiol, dodecanethiol, hexylphosphonic acid (HPA), tetradecylphosphonic acid (TDPA), octylphosphonic acid (OPA), or combinations thereof.

(31) The first organic solvent may be, for example, cyclohexane, hexane, chloroform, toluene, octane, chlorobenzene, or a mixture thereof.

(32) The nanoparticle in the first dispersion may be, for example, any nanoparticle, such as a quantum dot, a metal NC, a magnetic NC, an oxide NC, a nanowire, or a nanoplate.

(33) Particular examples of the quantum dot may include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, CdHgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, SnPbSTe, Si, Ge, SiC, SiGe, or a combination thereof. The quantum dot may, for example, have a core-shell structure or a core-shell-shell structure.

(34) For example, Zn.sub.2S.sub.2, Zn.sub.2Se.sub.2, Zn.sub.2Te.sub.2, Cu.sub.2S.sub.2, Cu.sub.2Se.sub.2, Cu.sub.2Te.sub.2, Mn.sub.2S.sub.2, Mn.sub.2Se.sub.2, Mn.sub.2Te.sub.2, Fe.sub.2S.sub.2, Fe.sub.2Se.sub.2, Fe.sub.2Te.sub.2, Co.sub.2S.sub.2, Co.sub.2Se.sub.2, and Co.sub.2Te.sub.2 may be used as the cationic MCC in the second solution.

(35) The second organic solvent in the second solution is an organic solvent that may respectively dissolve and disperse the cationic MCC and the nanoparticles. The second organic solvent may be, for example, ethanolamine, DMSO, DMF, formamide, water, hydrazine, hydrazine hydrate, or a mixture thereof.

(36) The first organic ligand coordinated to the nanoparticles may be substituted with the cationic MCC by stirring the mixed solution obtained by mixing the first dispersion and the second solution, and as a result, nanoparticles passivated with the cationic MCC are formed.

(37) According to an embodiment, the mixed solution may be phase separated into a first organic solvent layer from the first dispersion and a second organic solvent layer from the second solution. In this case, the nanoparticles in the first dispersion are transferred to the second organic solvent layer by stirring the mixed solution and the first organic ligand passivating the nanoparticles may be exchanged with the cationic metal-chalcogenide.

(38) The stirring of the mixed solution obtained by mixing the first dispersion and the second solution may be, for example, performed at a temperature ranging from about 20° C. to about 150° C.

Example 1—Zn2Se2 Synthesis

(39) 3 g (38 mmol) of Se and 9 g (23.8 mmol) of NaBH.sub.4 were added into 100 g of ethanol, while a reaction flask having the above mixture contained therein was put into an ice bath such that a temperature of the mixture was not permitted to rise above 20° C. A first reaction mixture thus obtained was reacted while being stirred while being refluxed in a nitrogen atmosphere. The reaction temperature was 80° C., a reaction pressure was atmospheric pressure, and a reaction time was 1.5 hours. As a result, a second reaction mixture containing Na.sub.2Se.sub.2 was obtained. 4.5 g of Na.sub.2Se.sub.2 was obtained from the second reaction mixture by removing by-products and allowing only Na.sub.2Se.sub.2 to remain by using vacuum at room temperature.

(40) FIG. 2 illustrates the results of 77 Se nuclear magnetic resonance (NMR) analysis of Na.sub.2Se.sub.2 obtained from the second reaction mixture. In the analysis process, methanol substituted with heavy hydrogen was used as a solvent. As illustrated in FIG. 2, a doublet was detected between −536 and −538 and a singlet was detected at −547. The singlet detected at −547 indicated that Na.sub.2Se.sub.2 was formed, and the doublet detected between −536 to −538 indicated that NaHSe, a by-product, was formed.

(41) Next, 0.043 g (0.2 mmol) of Na.sub.2Se.sub.2 and 0.121 g (0.8 mmol) of Zn(ClO.sub.4).sub.2 were respectively dissolved in 4 g of ethanol. A reaction was performed by dropwise putting a Zn(ClO.sub.4).sub.2 ethanol solution into an Na.sub.2Se.sub.2 ethanol solution. A third reaction mixture thus obtained was centrifuged to obtain a fourth reaction mixture containing Zn.sub.2Se.sub.2(ClO.sub.4).sub.2. 0.4 g of Zn.sub.2Se.sub.2(ClO.sub.4).sub.2 was obtained from the fourth reaction mixture. The Zn.sub.2Se.sub.2(ClO.sub.4).sub.2 thus obtained was dissolved in ethanolamine.

(42) FIG. 3 illustrates the results of 77 Se NMR analysis of Zn.sub.2Se.sub.2(ClO.sub.4).sub.2 obtained from the fourth reaction mixture. In the analysis, the sample used was a sample obtained by dissolving the obtained Zn.sub.2Se.sub.2(ClO.sub.4).sub.2 in ethanolamine and then dissolving it further in DMSO substituted with heavy hydrogen. Singlets were detected at 626 and 874. For comparison, 77Se NMR analysis was conducted on a sample obtained by dissolving Na.sub.2Se.sub.2 obtained from the second reaction mixture in DMSO substituted with heavy hydrogen, and the results thereof are presented in FIG. 4. In FIG. 4, a singlet was detected at 547 ppm. By comparing FIG. 3 and FIG. 4, it may be understood that Na.sub.2Se.sub.2 reacted with Zn(ClO.sub.4).sub.2.

(43) Next, 0.2 g of Zn.sub.2Se.sub.2(ClO.sub.4).sub.2 was dissolved in 4 g of ethanolamine. A fifth reaction mixture thus obtained was reacted while stirring. The reaction temperature was 60° C., the reaction pressure was atmospheric pressure, and the reaction time was 1.5 hours. As a result, a sixth reaction mixture containing Zn.sub.2Se.sub.2 was obtained.

(44) FIG. 5 illustrates the results of fast atom bombardment-mass spectroscopy (FAB-MASS) analysis of the sixth reaction mixture. A singlet was detected at 487, which is the calculated molecular weight of Zn.sub.2Se.sub.2(ClO.sub.4).sub.2, and as a result, it may be understood that Zn.sub.2Se.sub.2 was formed. A molecular weight of 408 represents ethanolamine-Zn.sub.2Se.sub.2, which was formed by the reaction of Zn.sub.2Se.sub.2(ClO.sub.4).sub.2 with ethanolamine.

Example 2—Preparation of Quantum Dots Passivated with Zn2Se2

(45) 18 mg of Zn.sub.2Se.sub.2 obtained in Example 1 was dissolved in 3 ml of ethanolamine to prepare an MCC solution. A quantum dot dispersion was prepared in which 1 wt % of CdSe (average particle diameter of 4 nm) was dispersed in hexane. 0.1 ml of the MCC solution was added to 3 ml of DMSO to prepare an MCC/DMSO solution. 6 g of the MCC/DMSO solution, 1 ml of the quantum dot dispersion, and 5 g of hexane were mixed and then stirred at room temperature for 3 hours. CdSe quantum dots in a hexane layer were gradually transferred to a DMSO layer, through a ligand-exchange process (see FIG. 6), and quantum dots passivated with cationic metal-chalcogenide (Zn.sub.2Se.sub.2—CdSe) were formed. Zn.sub.2Se.sub.2—CdSe was precipitated using butanol to obtain 5 mg of Zn.sub.2Se.sub.2—CdSe.

(46) FIG. 7 illustrates the results of surface zeta potential analysis of CdSe quantum dots passivated with Zn.sub.2Se.sub.2. It may be understood that CdSe quantum dots before the modification with MCC had neutral surface charges, whereas CdSe quantum dots passivated with Zn.sub.2Se.sub.2 had a positive charge of 169 mV. FIG. 8 is an ultraviolet (UV) absorption spectrum of CdSe quantum dots passivated with Zn.sub.2Se.sub.2. It may be understood that these characteristics of the CdSe quantum dots were not changed after the passivation with Zn.sub.2Se.sub.2.

(47) As described above, according to the one or more above embodiments disclosed herein, the present disclosure enables the passivation of nanoparticles by a cationic MCC. The phrase “passivation of nanoparticles by a cationic MCC” means that nanoparticles having material characteristics and surface charge characteristics that may be difficult to be passivated with a typical anionic MCC may be passivated. Also, with respect to the passivation of nanoparticles by a cationic MCC disclosed herein, the use of hydrazine, which has relatively strong toxicity and explosiveness, may be avoided (i.e., hydrazine may not be used). In addition, since a cationic MCC has a structure complementary to an anionic MCC, a new material that may not be prepared with an anionic MCC may be prepared. Further, since nanoparticles passivated with a cationic MCC may have positive charges on the surfaces thereof, the nanoparticles may be used in forming a composite structure of cationic MCC nanoparticles-anionic MCC nanoparticles by using electrostatic attraction in the future.

(48) It should be understood that the exemplary embodiments described herein are descriptive only and are not intended to limit the present disclosure. Descriptions of features or aspects within each embodiment should typically be considered as being available for other similar features or aspects in other embodiments.