JP2021075441A - Wurtzite type sulfide nanoparticle, and method of synthesizing the same - Google Patents

Abstract

To provide a method of synthesizing a wurtzite type sulfide nanoparticle by chemical synthesis, and to synthesize a ZnOS nanoparticle having an even and high oxygen composition.SOLUTION: The sulfide nanoparticle having a wurtzite type crystal structure is synthesized by subjecting a II group element material containing at least zinc, and a sulfur material to heat decomposition in a solvent. At this time, as additive agents, there are added a first additive agent composed of at least one material of a polyol material, and an ethylene glycol stearate material, and a second additive agent for suppressing a particle size by coordinating on a surface of the nanoparticle during reaction to a reaction system.SELECTED DRAWING: Figure 3

Description

The present invention relates to wurtzite type (WZ type) sulfide nanoparticles and a method for synthesizing the same, and more particularly to a technique for producing WZ type zinc sulfide nanoparticles of 10 nm or less with high purity.

Since zinc sulfide, which is a group II-VI compound semiconductor material, and ZnOS nanoparticles obtained by adding oxygen to zinc sulfide have an energy gap from visible to ultraviolet, phosphors, EL (electroluminescence) materials, solar cells, etc. It is a promising material as an optoelectronic material for gas, chemical, biosensors, etc.

In general, semiconductor nanoparticles can exhibit a quantum effect and widen the energy gap by making the particle size smaller than the Bohr radius. ZnS has a Bohr radius of 2.5 nm, and by setting the particle size to 5 nm or less, a wide wavelength range can be realized as a light emitting / receiving material. As a method for synthesizing zinc sulfide nanoparticles, a production method by chemical synthesis has been established, and an example of production of zinc sulfide nanoparticles having a diameter of 5 nm or less is reported in, for example, Patent Document 1. In the technique described in Patent Document 1, the particle size is controlled by chemically bonding to the surface of nanoparticles by using a surfactant such as an organic carboxylic acid, an organic nitrogen compound or an organic sulfur compound as an additive at the time of synthesis. It is disclosed to do.

By the way, ZnS is known to have a cubic crystal structure called a sphalerite type as a stable crystal structure and a hexagonal crystal structure of a wurtzite type as a semi-stable crystal structure. Cubic zinc sulfide has high symmetry, so defects in the crystal are easily propagated and deterioration is severe due to heat and humidity, whereas wurtzite type zinc sulfide has higher symmetry than sphalerite type. Since it is low, it is expected as an optical material with high reliability because the propagation of defects is suppressed.

It is known that the wurtzite-type zinc sulfide can be obtained by heat-treating zinchalerite-type zinc sulfide at a temperature of 1020 ° C. or higher, but a conventional method for synthesizing nanoparticles (for example, Patent Document 1). In the synthesis method), zinchalerite-type zinc sulfide having a stable crystal structure is produced, and wurtzite-type zinc sulfide nanoparticles cannot be obtained.

On the other hand, ZnOS particles obtained by mixing oxygen with zinc sulfide are expected to change the energy gap widely by changing the amount of oxygen added, but ZnS particles are highly immiscible, so the added element is added. It is difficult to add the mixture uniformly in the particles. Specifically, at a temperature of 1000 K or less, the solid solution limit of oxygen in ZnS is predicted to be 5% or less, and when the ratio of oxygen is increased by the conventional synthesis method, the ZnO phase and the ZnS phase are obtained. It has been separated, and ZnOS nanoparticles having a uniform and high oxygen composition have not been obtained.

JP-A-2009-233845

The first object of the present invention is to synthesize wurtzite-type sulfide nanoparticles by chemical synthesis, and the second object is to synthesize ZnOS nanoparticles having a uniform and high oxygen composition.

In order to solve the above problems, the present inventors have conducted diligent research, and as a result, when synthesizing zinc sulfide nanoparticles by chemical synthesis with a zinc material and a sulfur material, by using two kinds of additives at the same time as additives. Zinc sulfide nanoparticles of the wurtzite type with an average particle size of 10 nm or less can be obtained, and by adjusting the ratio of the zinc material and the sulfur material, ZnOS having a uniform crystal structure of the wurtzite type They have found that nanoparticles can be obtained and have reached the present invention.

In the present specification, the sulfide nanoparticles include nanoparticles composed of sulfides of Group II elements and sulfide nanoparticles doped with other elements.

That is, the first aspect of the present invention is a method of synthesizing sulfide nanoparticles having a wurtzite type crystal structure by thermally decomposing at least a group II element material containing zinc and a sulfur material in a solvent. The system is composed of a first additive consisting of at least one of a polyol-based material and an ethylene glycol-based stearate material as an additive, and a second additive that coordinates with the surface of the nanoparticles during the reaction to suppress the particle size. It is characterized by adding the additive of.

A second aspect of the present invention is sulfide nanoparticles having a wurtzite crystal structure represented by the following general formula.
(Zn) (S _1-x O _x )
(However, x> 0)
Sulfide nanoparticles having an average particle size of 10 nm or less.

Further, it is a sulfide nanoparticle having a wurtzite crystal structure represented by the following general formula.
Zn (S _1-x O _x )
(However, 0.4> x ≧ 0)
Wire-shaped sulfide nanoparticles having a minor axis of 4 nm or less, a major axis of 50 nm or less, and an aspect ratio of 5 or more and 25 or less.

According to the present invention, wurtzite-type sulfide nanoparticles having high reliability such as optical properties can be synthesized. Further, according to the present invention, sulfide nanoparticles in which sulfur in crystals is replaced with oxygen at a relatively high ratio are provided. This makes it possible to control the energy gap of zinc sulfide and expand the range of applications.

(A) is a diagram showing a TEM image of zinc sulfide nanoparticles of Example 1, and (B) is a diagram showing a TEM image of zinc sulfide nanoparticles of Comparative Example 1. The figure which shows the XRD pattern of Example 1 and Comparative Example 1. (A) is a diagram showing a TEM image of zinc sulfide nanoparticles of Example 2, and (B) is a diagram showing a TEM image of zinc sulfide nanoparticles of Example 3. The figure which shows the XRD pattern of Examples 1, 2, 3 and the reference example.

Hereinafter, the method for synthesizing the sulfide nanoparticles of the present invention will be described.
In the method for synthesizing sulfide nanoparticles of the present invention, there are two types of additives when synthesizing sulfide nanoparticles (MS, MOS) by chemical synthesis with a group II element (described as M) material and a sulfur material. Additives are used at the same time.

Examples of the group II element (M) include zinc (Zn) and cadmium (Cd), and it is preferable to use a complex of these. For example, as the zinc material, a zinc complex such as zinc _{acetate (Zn (AC) 2} ), zinc stearate (ST-Zn), zinc acetylacetonate (Zn (ACAC) ₂ ), zinc chloride (ZnCl _{2) is used.} Acetylacetonate zinc is particularly preferable. Similarly, for cadmium, a complex such as cadmium distearate, acetylacetonate cadmium, or cadmium chloride can be used. In the following description, a case where the Group II element is Zn will be described as an example.

Examples of the sulfur material include thiol-based materials such as dodecanethiol and hexadecanethiol, 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, and 1,1-dibutylthiourea. S-containing organic compounds such as 1,3-dibutylthiourea, thioacetamide, and tetramethylthiourea, and sulfur powder can be used. In particular, 1,1-dibutylthiourea or 1,3-dibutylthiourea is preferable.

The ratio between the group II element material (zinc material) and the sulfur material can be the stoichiometric ratio of the sulfide nanoparticles, but by controlling the S / Zn ratio, the shape of the nanoparticles can be changed at the same time. It can be controlled from a shape to a sphere. Specifically, when the S / Zn ratio is 1, wire-like particles having a short side of 2 to 4 nm, a long side of 5 to 50 nm, and an aspect ratio of 5 to 25 can be produced, and the S / Zn ratio is 2. At this time, spherical particles having a particle size of 2 to 5 nm and an aspect ratio of 5 or less can be produced. By aligning the long side directions of the wire-shaped particles, it is possible to impart polarization property depending on the shape of the wire-shaped particles, and the wire-shaped particles can be applied to optical applications different from the conventional spherical particles.

On the other hand, by making the S / Zn ratio less than 1, that is, the amount of S less than Zn, sulfide nanoparticles in which a part of S is replaced with oxygen can be obtained. Specifically, by setting the S / Zn ratio to y (however, 1> y), O is taken in by the insufficient S amount. In this case, when S / Zn is 0.4 or less, sulfide nanoparticles in which the ZnS phase and the ZnO phase are mixed are generated. Therefore, the S / Zn ratio is preferably more than 0.4. More preferably, it is 6 or more. By setting S / Zn to 0.6 or more, nanoparticles having a size of 10 nm or less can be obtained.

One of the two types of additives, the first additive, is a polyol-based material such as hexadecanediol, tetraethylene glycol, propylene glycol, trimethyl glycol, diethylene glycol, ethylene glycol, stearyl glycol, and ethylene glycol stearate. Use at least one of the materials. Of these, ethylene glycol is particularly preferable. The amount of the first additive may be extremely small, and is about 0.5% by volume with respect to the solvent. Further, if the amount added is large, it causes not only the reaction system but also bumping and the like, so it is preferably 1% by volume or less, more preferably 0.8% by volume or less.

As the second additive, a complex that coordinates Zn with ZnS particles and is bulky is preferable, and for example, trioctylphosphine sulfide (hereinafter referred to as TOP: S) can be used. TOP: S is a complex in which sulfur (S) is bonded to the phosphorus atom (P) of trioctylphosphine by a coordination bond, and can be synthesized from trioctylphosphine and sulfur. TOP: S is a sulfur-containing complex and is known as a raw material for sulfur-containing nanoparticles, but in the reaction of the present invention, it does not function as a source of sulfur, but as a first additive. It is considered that the combined use of these substances has a function of suppressing the size of particles while maintaining the Wurtz-shaped crystal structure.

The amount of the second additive is 0.1 to 1.0, preferably 0.2 to 0.8, and more preferably about 0.4 to 0.6 in terms of molar ratio with respect to the zinc raw material. Further, when a complex is synthesized with trioctylphosphine and sulfur and put into the reaction system, it is preferable to increase the amount of trioctylphosphine in a stoichiometric ratio. This prevents excess sulfur from entering the reaction system and causing unintended substitution with oxygen.

As the solvent, since the reaction is carried out at a relatively high temperature, a solvent having a boiling point (bp) higher than the reaction temperature is used. Specifically, oleylamine (bp: 350 ° C.), benzylbenzoate (bp: 350 ° C.), 1-octadecene (bp: 179 ° C. (under 15 mmHg)), oleic acid (b. p .: 360 ° C.), trioctylphosphine oxide (bp .: 202 ° C. (below 2 mmHg)), trioctylphosphine (bp: 445 ° C.) can be used. In particular, oleylamine having a high boiling point is preferable.

The reaction is carried out by heating in a solvent (liquid phase). At this time, a multi-step reaction including a step of reacting at a relatively low temperature under reduced pressure (first step) and a step of reacting at a relatively high temperature under an inert atmosphere (second step) is performed. It is preferable to make the conditions such as reaction time and atmosphere different for each stage.

The reaction temperature in the first step is preferably 200 ° C. or lower. By setting the temperature to 200 ° C. or lower, it is possible to suppress the formation of sphalerite-type crystals.

The first step, for example, firstly the temperature was raised After brief holding less than 1 hour in an inert atmosphere at 100 ° C. below the temperature (for example, about 70 ° C.) such as N _2, of 200 ° C. or less under a reduced pressure atmosphere The reaction proceeds at temperature (eg 130 ° C.). The pressure under the reduced pressure atmosphere is 1/100 or less of the atmospheric pressure (about 100 kPa). However, it should be 15 Pa or more to prevent the solvent from suddenly boiling. The reaction time of the reaction carried out in a reduced pressure atmosphere and 200 ° C. or lower is about 1 to 3 hours.

The second step is held under an inert atmosphere at a temperature higher than the reaction temperature of the first step, 200 ° C. or higher and below the boiling point of the solvent (for example, 250 ° C.) for 1 to 2 hours. The temperature rising rate from the first step to the second step is not limited, but is set to, for example, 50 ° C./5 min. In the second step, the nuclei of the crystals produced in the first step are grown. If the nucleus of a hexagonal (WZ type) crystal is generated in the first step, the crystal system is maintained even if the temperature is raised thereafter, and the remaining reaction is rapidly promoted by raising the temperature. Can be done. After the second step, the temperature may be further increased (but below the boiling point of the solvent) and held for a short period of time, which allows the reaction to be completed quickly.

After completion of the reaction, the temperature is lowered, and the nanoparticles are recovered by the same method as the method for recovering nanoparticles by a general thermal decomposition method. Specifically, a predetermined solvent such as hexane is added to the reaction solution after the temperature is lowered to diffuse the mixture, and then a poor solvent is added to aggregate the particles and centrifuge them. This process may be repeated a plurality of times as needed. Finally, particle cleaning is performed to obtain a dispersion of nanoparticles.

According to the method for producing sulfide nanoparticles of the present invention, by adding two kinds of additives to the reaction system, a plurality of problems of controlling the crystal system of nanoparticles and alleviating immiscibility can be solved at once. This makes it possible to provide wurtzite-type sulfide nanoparticles having a size of 10 nm or less, which could not be produced by conventional chemical synthesis. Regarding the uptake of other elements, the oxygen concentration of sulfide can be increased to about 40 atomic%.

Typical sulfide nanoparticles obtained by the method for producing sulfide nanoparticles of the present invention are Zn ( _Ox S _1-x ) having a wurtzite type crystal structure having a particle size of 10 nm or less (however, 0.4> x). _{> 0) Nanoparticles and wire-shaped Zn (Ox} S _1-x ) (however, 0.4> x ≧ 0) nanoparticles having a minor axis of 4 nm or less, a major axis of 50 nm or less, and an aspect ratio of 5 or more and 25 or less. Including.

Hereinafter, an example of synthesizing the sulfide nanoparticles of the present invention will be described.

<Example 1>
Oleylamine 10mL as a solvent, a zinc material as _Zn (ACAC) 2 2.0mmol, using 1,3-dibutylthiourea 2.0mmol as sulfur material, ethylene glycol (EG) 1.0 mmol as the first additive, the second TOP-S (TOP 1.2 mmol and sulfur 0.6 mmol) was used as an additive. The S / Zn ratio of the zinc material and the sulfur material (excluding TOP-S) is 1.

After filling the container (100 mL) with the material, the material was kept at 70 ° C. for 30 minutes in a nitrogen atmosphere, then heated and held at 130 ° C. for 2 hours in a reduced pressure atmosphere. The pressure at this time was about 100 Pa (10 Pa or more and 1000 Pa or less). Thereafter, the temperature was raised at a heating rate of 50 ° C. / 5 minutes, after which was held for 2 hours at 250 ° C. under N _2, was synthesized held at 300 ° C. under a N ₂ atmosphere and further raising the temperature ..

After lowering the temperature, 5 ml of hexane was added to the reaction solution, and the mixture was stirred and then collected in a centrifuge tube. The particles were aggregated by adding ethanol, which is a poor solvent, and precipitated using a centrifuge. The separation condition was 12,000 rpm for 60 minutes. After discarding the supernatant, 5 mL of hexane was added and stirred with a shaker for 30 minutes to disperse the particles. Ethanol was added again, and the same process was repeated once more to wash the particles to obtain a dispersion of ZnS nanoparticles.

<Comparative example 1>
Zinc sulfide nanoparticles were synthesized in the same manner as in Example 1 except that two kinds of additives were not used.

The transmission electron microscope images (TEM images) of the particles obtained in Example 1 and Comparative Example 1 are shown in FIGS. 1 (A) and 1 (B), respectively. As shown in FIG. 1 (A), it was confirmed that the shape of the particles was wire-like, the minor axis was 2 to 3 nm, and the major axis was 20 to 50 nm. On the other hand, when no additive was used, spherical particles having a particle size of 4 to 5 nm were obtained as shown in FIG. 1 (B).

The XRD diffraction patterns of the particles obtained in Example 1 and Comparative Example 1 are shown in FIG. As shown in FIG. 2, the particles of Comparative Example 1 had three peaks of cubic (111), (220) and (311), and it was confirmed that they were sphalerite-type zinc sulfide. It was. On the other hand, the particles of Example 1 have six peaks of hexagonal (100) (002) (101) (102) (110) (103) (112) and are of the wurtzite type ZnS. Was confirmed.

<Examples 2 and 3 and reference example>
The amount of 1,3-dibutylthiourea used as a sulfur material was changed to 1.6 mmol (Example 2), 1.2 mmol (Example 3), and 0.8 mmol (reference example), respectively, and the others were used. , Zinc sulfide nanoparticles were synthesized in the same manner as in Example 1.

The TEM images of Examples 2 and 3 are shown in FIG. 3, and the XRDs of Examples 2, 3 and Reference Examples are shown in FIG. From the TEM images, spherical nanoparticles were confirmed in all of Examples 2 and 3, and the particle sizes were 2 to 3 nm (Example 2) and 3 to 4 nm (Example 3), respectively. Further, from the XRD pattern, it was confirmed that the nanoparticles of Examples 3 and 4 were uniform wurtzite-type ZnOS particles. Further, as a result of XRD analysis, when Example 1 has a sulfur material concentration of 100%, ZnO _0.1 S _0.9 is produced in Example 3 having a sulfur material concentration of 80%, and the sulfur material concentration is 60%. In Example 4, ZnO _0.2 S _0.8 was produced, and it was confirmed that the sulfur of the ZnOS particles was replaced with oxygen according to the amount of the raw material used. On the other hand, in the reference example (sulfur material concentration 40%), the wurtzite-type ZnOS was hardly generated, and as can be seen from the XRD pattern in FIG. 4, the peak of the cubic ZnS and the peak of the hexagonal ZnO were observed. Was done.

According to the present invention, novel nanoparticles that can be applied as an optical material, a magnetic material, an electric material, a phosphor, or the like are provided.

Claims (11)

It is a method of synthesizing sulfide nanoparticles having a wurtzite crystal structure by thermally decomposing a group II element material containing at least zinc and a sulfur material in a solvent.
In the reaction system, as an additive, a first additive consisting of at least one of a polyol-based material and an ethylene glycol-based stearate material is coordinated with the surface of the nanoparticles during the reaction to suppress the particle size. A method for synthesizing sulfide nanoparticles, which comprises adding the second additive. The method for synthesizing sulfide nanoparticles according to claim 1.
The first step of reacting under reduced pressure at a first temperature below 200 ° C.
A method for synthesizing sulfide nanoparticles, which comprises a second step of continuing the reaction to generate sulfide nanoparticles at a second temperature higher than the first temperature under atmospheric pressure. The method for synthesizing sulfide nanoparticles according to claim 1.
A method for synthesizing sulfide nanoparticles, wherein the first additive is ethylene glycol. The method for synthesizing sulfide nanoparticles according to claim 1.
A method for synthesizing sulfide nanoparticles, wherein the second additive is trioctylphosphine sulfide. The method for synthesizing sulfide nanoparticles according to claim 1.
Sulfide nanoparticles characterized by producing wire-shaped nanoparticles using the group II element material and the sulfur material (excluding sulfur contained in the additive) at a stoichiometric ratio of zinc sulfide. How to synthesize particles. The method for synthesizing sulfide nanoparticles according to claim 1.
The ratio of the sulfur material (excluding sulfur contained in the additive) to the group II element material is equal to or more than the chemical quantitative ratio of the group II element sulfide, and spherical nanoparticles are produced. Method for synthesizing sulfide nanoparticles. The method for synthesizing sulfide nanoparticles according to claim 1.
The ratio of the sulfur material (excluding sulfur contained in the additive) to the group II element material is less than the chemical quantitative ratio of zinc sulfide, and a part of sulfur in the sulfide is replaced with oxygen. A method for synthesizing sulfide nanoparticles, which comprises producing particles. It is a sulfide nanoparticle having a wurtzite crystal structure represented by the following general formula.
Zn (O _x S _1-x )
(However, x> 0)
Sulfide nanoparticles with a maximum particle size of 10 nm or less. The sulfide nanoparticles according to claim 8, wherein x <0.4 in the general formula. The sulfide nanoparticles according to claim 8 or 9, wherein the maximum particle size is 5 nm or less. It is a sulfide nanoparticle having a wurtzite crystal structure represented by the following general formula.
Zn (O _x S _1-x )
(However, 0.4> x ≧ 0)
Wire-shaped sulfide nanoparticles with a minor axis of 4 nm or less, a major axis of 50 nm or less, and an aspect ratio of 5 or more and 25 or less.

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