KR20180096252A - Method of fabricating FeS2 nanocrystals - Google Patents

Abstract

The present invention provides a method for manufacturing FeS_2 nanocrystals. The method comprises: a first step of preparing a solution of Fe-surfactant precursor in which iron halide salt and primary amines are mixed and preparing a solution of S-precursor in which sulfur is mixed with secondary amines; and a second step of injecting and heating the S-precursor solution into the Fe-surfactant precursor solution and growing the FeS_2 nanocrystals. The purity and shape of the FeS_2 nanocrystals are controlled according to the concentration of H_2S formed in the second step. According to the present invention, a method for manufacturing FeS_2 capable of controlling the purity and shape of FeS_2 nanocrystals can be realized.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method for fabricating FeS2 nanocrystals,

The present invention relates to a method for producing FeS ₂ . More particularly, the present invention relates to a method for producing FeS ₂ nanocrystals.

Iron disulfide (iron pyrite, FeS ₂ ) is attracting attention as an energy element because of its low toxicity, abundant reserves and low production cost of raw materials. However, it is liable to contain impurities such as mackinawite (FeS), marcasite (orthor-FeS ₂ ) and greigite (Fe ₃ S ₄ ), and the surface stability is poor. For further information, please refer to the following publications.

C. Steinhagen, T.B. Hatvey, C.J. Stolle, J. Harris, B.A. Korgel, Pyrite nanocrystal solar cells: promising, or fool's Gold, J. Phys. Chem. Lett. 3 (2012) 2352-2356.

The present invention provides a FeS ₂ nanocrystal capable of controlling the purity and shape of FeS ₂ nanocrystals to solve various problems including the above problems. However, these problems are illustrative and do not limit the scope of the present invention.

A method for producing FeS ₂ nanocrystals according to one aspect of the present invention is provided. The FeS ₂ nanocrystal may be prepared by preparing a Fe-surfactant precursor solution obtained by mixing the iron hydrate salt and the first amines, adding a sulfur precursor (S-precursor) obtained by mixing sulfur with a second amine, ) Solution; And injecting and heating the sulfur-precursor solution into the iron-surfactant precursor solution to thereby grow FeS ₂ nanocrystals; And the purity and shape of the FeS ₂ nanocrystal are controlled according to the concentration of H ₂ S formed in the second step.

In the FeS ₂ nanocrystals, the iron hydrate salt includes FeCl ₂ .4H ₂ O (Iron (II) chloride tetrahydrate), the first amines include octadecylamine (ODA) The secondary amines may include oleylamine (OLA) or trioctylamine (TOA).

In the FeS ₂ nanocrystals, when the second amines include oleylamine (OLA), the FeS ₂ nanocrystal may have a spherical shape.

In the FeS ₂ nanocrystals, when the second amines include trioctylamine (TOA), the FeS ₂ nanocrystals may have a cubic shape.

A method for manufacturing FeS ₂ nanocrystals according to another aspect of the present invention is provided. The FeS ₂ nanocrystals are prepared by mixing and stirring FeCl ₂ .4H ₂ O (Iron (II) chloride tetrahydrate), octadecylamine (ODA) and trioctylamine (TOA) (Fe-surfactant precursor) solution; Preparing sulfur-precursor solution by mixing sulfur with oleylamine (OLA) or trioctylamine (TOA); Injecting the sulfur-precursor solution into the iron-surfactant precursor solution, heating the solution, and stirring the solution in a nitrogen atmosphere at a heating temperature to grow FeS ₂ nanocrystals; And cooling the mixed solution in which the FeS ₂ nanocrystals are grown and purifying the FeS ₂ nanocrystals by precipitation by adding chloroform to the FeS ₂ nanocrystals, wherein the amount of the FeS ₂ nanocrystals is controlled by adjusting the amount of the octadecylamine (ODA) ₂ nanocrystals, and when the sulfur-precursor solution contains oleylamine (OLA), the FeS ₂ nanocrystals have a shape that is spherical rather than cubic, When the sulfur-precursor solution contains trioctylamine (TOA), the FeS ₂ nanocrystal has a cubic shape rather than a spherical shape.

According to an embodiment of the present invention as described above, FeS ₂ nanocrystals can be fabricated which can control the purity and shape of FeS ₂ nanocrystals. Of course, the scope of the present invention is not limited by these effects.

FIG. 1 shows the XRD analysis results of the iron sulfide nanoparticles according to the amount of octadecylamine (ODA).
Figure 2 is a TEM image (a), HRTEM images (b) and size distribution (c), the TEM image (d), HRTEM image (e) and size distribution (f) of the FeS ₂ nano-spheres of the FeS ₂ nano cube .
FIG. 3 is a TEM image of the growth process of cubic FeS ₂ nanocrystals (a) and spherical FeS ₂ nanocrystals (b) according to various durations.
Figure 4 is an HRTEM image of cubic FeS ₂ nanocrystals (a) and spherical FeS ₂ nanocrystals.
XRD of the nano-cube and nano-spheres of Figure 5 FeS ₂ nanocrystals (a), Raman spectrum (b), spherical (spherical) Fe ₂ p XPS spectrum of _{FeS 2 (c), S 2} p XPS spectra (d) , The Fe ₂ p XPS spectrum (e) and the S ₂ p XPS spectrum (f) of the cubic FeS ₂ .
Figure 6 shows the optical properties of FeS ₂ nanocrystals.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms as used herein include plural forms as long as the phrases do not expressly express the opposite meaning thereto. Means that a particular feature, region, integer, step, operation, element and / or component is specified, and that other specific features, regions, integers, steps, operations, elements, components, and / And the like.

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. Commonly used predefined terms are further interpreted as having a meaning consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or very formal meanings unless defined otherwise.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

The FeS ₂ nanocrystals according to an embodiment of the present invention may be prepared by mixing FeCl ₂ .4H ₂ O (Iron (II) chloride tetrahydrate), octadecylamine (ODA) and trioctylamine Stirring the solution to prepare an iron-surfactant precursor solution; Preparing sulfur-precursor solution by mixing sulfur with oleylamine (OLA) or trioctylamine (TOA); Injecting the sulfur-precursor solution into the iron-surfactant precursor solution, heating the solution, and stirring the solution in a nitrogen atmosphere at a heating temperature to grow FeS ₂ nanocrystals; And cooling the mixed solution in which the FeS ₂ nanocrystals are grown, and adding chloroform to refine the FeS ₂ nanocrystals by a precipitation reaction.

In particular, it is possible to control the purity and geometry (shape) of the FeS ₂ nanocrystals according to the concentration of H ₂ S formed in the step in which the FeS ₂ nanocrystal growth. Also, the purity of the FeS ₂ nanocrystals is controlled by controlling the amount of the octadecylamine (ODA), and when the sulfur-precursor solution contains oleylamine (OLA), the FeS ₂ nanocrystals When the shape of the FeS ₂ nanocrystal is spherical rather than cubic and the solution of the sulfur-precursor includes trioctylamine (TOA), the FeS ₂ nanocrystal has a shape of spherical ) Is cubic rather than cubic.

Hereinafter, an experimental example in which the above-described technical idea is implemented will be described in detail.

chemical substance

The present inventors have found that iron (II) chloride tetrahydrate (FeCl ₂ .4H ₂ O, 99%), octadecylamine (ODA), sulfur (S, 98% Amine (OLA; oleylamine, 70%) and trioctylamine (TOA, 90%) were prepared. Chloroform and methanol were also prepared. No additional purification was performed on the chemical in this experiment.

FeS ₂  Manufacture of nanocrystals

1 mmol of FeCl ₂ .4H ₂ O (Iron (II) chloride tetrahydrate), 10 g of octadecylamine (ODA) and 10 ml of trioctylamine were placed in a flask, For 1 hour to form an iron-surfactant precursor.

Separately, 0.192 g of elemental sulfur was added to 5 ml of oleylamine (OLA) to form a spherical S-precursor to form spherical FeS ₂ (S-precursor) for the formation of cubic FeS ₂ by dissolving 0.192 g of elemental sulfur in 5 ml of trioctylamine (TOA) Prepared. The mixture was stirred vigorously at a temperature of 70 < 0 > C at atmospheric pressure until the sulfur was completely dissolved.

Subsequently, the sulfur-precursor solution is the iron-surfactant precursor solution was rapidly injected (injection) in, and stirring was continued to FeS ₂ nanocrystals for two hours and the heating temperature in a nitrogen atmosphere and then heated to 220 ℃ (iron pyrite nanocrystals ) To grow sufficiently. Thereafter, it is cooled to room temperature. The FeS ₂ nanocrystals can be purified by mixed solvent precipitation using chloroform and methanol in a centrifuge at 6000 rpm for 10 minutes. The purified nanocrystals are stored in chloroform. This manufacturing method can be understood as a modified hot injection method.

To investigate the effect of octadecylamine (ODA) on the phase change of iron sulfide, trioctylamine (TOA) was used as the solvent of the sulfur precursor and the amount of octadecylamine (ODA) Were set to 0 g, 2 g, 5 g, and 10 g, respectively.

Results and Analysis

By changing the amount of octadecylamine (ODA), the phase purity of FeS ₂ nanocrystals could be secured. FIG. 1 shows the XRD analysis results of the iron sulfide nanoparticles according to the amount of octadecylamine (ODA). As the amount of octadecylamine (ODA) changes from 0 to 10 g, the phase of iron sulfide is changed to the pure FeS ₂ phase through the FeS and Fe ₃ S ₄ phases mixed from the FeS phase. The structures of Fe _(1-x) S, Fe ₃ S ₄ and FeS ₂ are hexagonal [JCPDS 00-020-0535], cubic [JCPDS 01-089-1999] and cubic [JCPDS 00-0024-0076]. Octadecylamine (ODA) plays an important role in influencing iron-sulfur phase expression. In the absence of octadecylamine (ODA), only pure FeS phase is formed at 220 ° C, despite increased reaction time. When the amount of octadecylamine (ODA) is increased to 2 g, the peak of Fe ₃ S ₄ appears and the FeS peak intensity decreases. When the amount of octadecylamine (ODA) is added up to 5 g, the strength of the Fe ₃ S ₄ phase is increased, and a peak of the FeS ₂ phase appears. When the amount of octadecylamine (ODA) is 10 g, the peak strengths of FeS phase and Fe ₃ S ₄ completely disappear and a pure FeS ₂ phase is realized. According to this, it can be confirmed that FeS ₂ formation is realized as the amount of octadecylamine (ODA) increases. As the formation of the iron pyrite phase progresses and completes, the signal on the FeS phase gradually decreases and disappears. The FeS phase serves as a precursor to form the intermediate phase Fe ₃ S ₄ and finally transforms into a pure FeS ₂ phase.

In this example, trioctylamine (TOA) is used as a solvent for the sulfur and iron precursors for the formation of FeS ₂ nanocrystals. Trioctylamine (TOA) is a tertiary amine that can not be combined with sulfur to form a new precursor. Thus, the role of octadecylamine (ODA) for the formation of iron sulfide may become apparent. On the other hand, trioctylamine (TOA) solvent provides a suitable base environment for the formation of pure FeS ₂ phase. The mechanism of formation of the pure FeS ₂ phase is based on the reaction expressed by the following formula.

[Chemical Formula 1]

(2)

(3)

[Chemical Formula 4]

In formula (1), when a sulfur source solution (sulfur element and trioctylamine (TOA)) is injected into the iron source solution, an FeS phase is formed. In formula (2), more active sulfur sources, hydrogen sulfide and amide, are formed compared to elemental sulfur. In the formulas (3) and (4), in the presence of amide and hydrogen sulfide, the FeS phase transforms into the FeS ₂ phase via the Fe ₃ S ₄ phase. Formulas (3) and (4) were first discovered by the present inventors. Fe ₃ S ₄ phase means a phase formed when Fe ₃ S ₄ to the active sulfur source is present only in an an bars, this different appearance FeS additional sulfur source, H ₂ S, and if the reaction. This means that the active sulfur source plays an important role as a driving force which is converted into FeS ₂ through Fe ₃ S ₄ in FeS. Since it is associated with the intermediate precipitation reaction, the FeS ₂ phase obtained does not form another iron sulfide phase after formation. Therefore, pyrite formation is understood as irreversible reaction.

The shape of the FeS ₂ nanocrystals is controlled by changing the stabilized solvent for the sulfur source. Figure 2 is a TEM image (a), HRTEM images (b) and size distribution (c), FeS _2, TEM image (d), HRTEM image (e) and size distribution (f) of the nano-spheres of the FeS ₂ nano cube . Figures 2 (a), 2 (b), 2 (d) and 2 (e) show TEM and HRTEM images of two different morphologies of pyrite nanocrystals. The lattice parameters of cubic and spherical nanocrystals correspond to a range of known values as measured from HRTEM. The use of trioctylamine (TOA) as the sulfur-stabilized solvent in elemental form yields cubic pyrithium while the use of oleylamine (OLA) as solvent forms spherical pyrithione nanocrystals . Referring to FIGS. 2 (c) and 2 (f), the nanocubes have an average edge length of 80 nm and the nanospheres have an average diameter of 30 nm.

To further understand the growth mechanism for controlling the shape of FeS ₂ nanocrystals, a mixture of sulfur and various solvents (TOA or OLA) was injected into the iron compound solution for various times. The Fe / S ratio was kept at 1/6. The results are shown in TEM. FIG. 3 is a TEM image of the growth process of cubic FeS ₂ nanocrystals (a) and spherical FeS ₂ nanocrystals (b) according to various durations . In the case of the growth of the FeS ₂ cube, trioctylamine (TOA) was used as the solvent to bind the elemental sulfur. Trioctylamine (TOA) is a tertiary amine that can not be reacted with sulfur to form an active sulfur source (amide or H ₂ S). After the S-TOA precursor is injected into the iron-amine solution, the reaction of sulfur with the primary amine octadecylamine (ODA) takes place. This reaction slowly forms an active sulfur source and causes a low nuclei concentration. Low nucleation concentrations result in slow growth and larger seeds (Fig. 3 (a)). Conversely, when sulfur is combined with the primary amine oleylamine (OLA) as a sulfur source, an active sulfur source is readily formed. This leads to high nucleation concentrations. The high nucleation concentration allows rapid growth and overall smaller seed formation (Fig. 3 (b)). Seed formation is commonly observed in the production of nanoparticles. The seeds tend to become coarse because they are covered by a weak surfactant (OLA, ODA). Attachment occurs rapidly in the early stages. Clusters forming spherical seeds are smaller than clusters forming cubic seeds.

FIG. 4 is an HRTEM image of cubic FeS ₂ nanocrystals (a) at 45 min reaction time and spherical FeS ₂ nanocrystals at 30 min reaction time. Referring to FIG. 4, the crystal plane and crystal orientation can be confirmed when adhesion occurs. When a cube is formed, parallel fingers having a distance of 2.7 A correspond to a lattice space of (100) planes (FIG. 4 (a)). The growth of large seeds occurs mainly on the (100) plane and implements a cubic shape. Defects are observed on the interplanar spacing between the two crystals, which may be a sign of the oriented attachment indicated by the white dotted line. When the spheres are formed, the parallel fingers having a distance of 2.4 A correspond to the lattice spaces of the (210) planes (FIG. 4 (b)). Under sulfur-rich conditions, the orientation growth of smaller seeds occurs primarily on the (210) plane and implements a faceted spherical shape.

The crystallinity and binding properties as well as the optical properties of FeS ₂ nanocrystals were investigated. XRD of the nano-cube and nano-spheres of Figure 5 FeS ₂ nanocrystals (a), Raman spectrum (b), spherical (spherical) Fe ₂ p XPS spectrum of _{FeS 2 (c), S 2} p XPS spectra (d) , The Fe ₂ p XPS spectrum (e) and the S ₂ p XPS spectrum (f) of the cubic FeS ₂ .

5 (a) shows an XRD pattern of nano-cube and nanospheres of FeS ₂ nanocrystals. All XRD peaks for cubic FeS ₂ nanocrystals are well matched to the index of pyrite FeS ₂ (JPCDS No.0171-0053) and the allowed lattice parameter is a = 5.428 ANGSTROM. All XRD peaks for spherical FeS ₂ nanocrystals are in good agreement with the index of pyrite FeS ₂ (JPCDS No. 0024-0076) and the allowed lattice parameter is a = 5.428 ANGSTROM. Signals of marcasite, greigite, and pyrrhotite corresponding to Fe _(1-x) S (x = 0 to 2) were not found in the XRD analysis and no other impurity phases were found. The Raman spectroscopy can be applied to confirm the net asterisks of the pyrite FeS ₂ cube and spheroids. Figure 5 (b) shows that the Raman spectrum is consistent with the oscillations of the Eg, Ag and Tg modes for pyrite FeS ₂ . In the oscillation mode, the sulfur atom moves perpendicular to the SS coupling axis. However, in the case of spherical FeS ₂ nanocrystals, the peak at 430 cm ^-1 is not apparent due to the smaller nanoparticles. FeS phase (210 and 280cm ^-1), and the Raman peak for the marcasite (323 and 387cm ^-1) does not clear the bar, which means that no impurity phase. As described above, HRTEM images of monocyte and spherical pyrite nanoparticles were identified in FIG. The grating distance of 5.4 A corresponds to a single grating structure of cubic and spherical particles. Furthermore, XPS was applied to confirm the elemental composition of the surface of the nanocrystals in the prepared state. 5 (b) to 5 (e) show high-resolution Fe ₂ p XPS peaks and S ₂ p XPS peaks at the surfaces of cubic and spherical FeS ₂ nanocrystals. High-resolution Fe 2p spectra of the two types of nanocrystals are predominantly pyrite peaks (Fe 2p 3/2, 707.3 eV and Fe 2p 1/2, 720 eV). The XPS spectrum of the sulfur S 2p peak of the pyrite FeS ₂ nanocrystals represents three kinds of sulfur. It is believed that the peak at the 165 eV position corresponds to a unique poly-sulfide due to the core-hole effect. The peak at 168.5 eV corresponds to the sulfur spectrum of the FeS ₂ nanocube surface due to sulfate (SO ₄ ^-2 ), which is understood to be formed by exposure of the pyrite to air. Based on the results of XRD, Raman, HRTEM and XPS analysis, it can be confirmed that the FeS ₂ nanocrystals in the prepared state have excellent crystallographic and phase purity.

Figure 6 shows the optical properties of FeS ₂ nanocrystals. 6 (a), the UV-Vis-NIR spectrum of the FeS ₂ nanocrystals shows the absorption edge at 1500 nm and the shoulder peak at 500 nm. The slowly increasing absorption properties of FeS ₂ nanocrystals reflect the indirect bandgap properties of the material. Figures 6 (b) and 6 (c) show the (? E) ⁿ dependence as a function of the incident line energy (E = h?). The indirect bandgap transitions of cubic and spherical FeS ₂ nanocrystals are 0.95 eV and 1.0 eV, respectively. The direct band gap transitions of cubic and spherical FeS ₂ nanocrystals are 1.5 eV and 3.2 eV, respectively. This broad range of optical absorption of FeS ₂ nanocrystals is a characteristic of electronic structures containing broad energy bands. The energy band levels in bulk pyrite consist of S p? * Bands and d-band manifolds. The direct or indirect band gap value of the pyrite is in the range of 0.9 to 3.6 eV. Additionally, differences in the size and growth facets of FeS ₂ nanocrystals can form other Brillouin zone folding. Zone folding can also change the photonic band structure and can affect the transferability to direct or indirect transitions. This explains the band gap difference between cubic and spherical FeS ₂ nanocrystals.

Various analyzes and results of the experimental examples of the present invention have been described so far. In conclusion, shape control of pure FeS ₂ phase was realized by understanding the formation mechanism of pyrite nanocrystals. The net formation of FeS ₂ was achieved by increasing the amount of octadecylamine (ODA). Octadecylamine (ODA) plays an important role in the formation of H ₂ S. The presence of H ₂ S makes possible the formation of pure FeS ₂ phase through the intermediate phase process on FeS phase and Fe ₃ S ₄ . Furthermore, the H ₂ S concentration influences the shape control of FeS ₂ nanocrystals by using trioctylamine (TOA) and oleylamine (OLA). Trioctylamine (TOA) and oleylamine (OLA) are solvents for dissolving a sulfur source. Growth in different facets of nanocrystals under different active sulfur conditions can be a major reason for oriented attachment that implements different shapes. Understanding and mechanisms of pure phase formation and shape control can contribute to the process of applying FeS ₂ nanocrystals and the improvement of the properties of materials.

To summarize the present invention again, pure phases of cubic and spherical FeS ₂ nanocrystals, each having an average size of 30 nm to 80 nm, are implemented through a hot injection method and its variants. In this case, trioctylamine (TOA) and oleylamine (OLA) were used as solvents to dissolve the sulfur source. The concentration of the active sulfur source (H ₂ S), which can be formed by the reaction between the sulfur element and the primary amine, can have a great influence on the formation of pure water phase and shape control. The chemically active sulfur source enables the formation of FeS ₂ phases via the Fe ₃ S ₄ phase on FeS. Furthermore, the active sulfur concentration is understood to be a major factor driving the orientation attachment which implements other FeS ₂ nanocrystals. FeS ₂ nanocrystals with excellent phase purity and optical properties can be applied to energy devices such as photoelectric conversion devices.

On the other hand, according to Article 30 of the Patent Act, the invention of the present application is claimed by the inventor's article (Journal of Crystal Growth 461 (2017) 53-59). In addition, the contents of the above-mentioned patent application are incorporated herein by reference in their entirety.

It will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the following claims.

Claims (5)

A first step of preparing a Fe-surfactant precursor solution obtained by mixing iron halide salt and primary amines and preparing a S-precursor solution in which sulfur is mixed with secondary amines; And
A step of injecting and heating the sulfur-precursor solution into the iron-surfactant precursor solution to thereby grow FeS ₂ nanocrystals; , ≪ / RTI &
Wherein according to the concentration of H ₂ S formed in Step 2, characterized in that to control the purity and geometry (shape) of the FeS ₂ nanocrystals, FeS ₂ nanocrystals method. The method according to claim 1,
The iron hydrate salts are FeCl ₂ · 4H ₂ O include (Iron (II) chloride tetrahydrate), the first amine is octadecylamine; include (ODA Octadecylamine), and the second amine is oleyl amine (OLA ; oleylamine) or trioctylamine (TOA; trioctylamine), FeS _2, characterized in that the nanocrystal comprising the method of manufacturing. 3. The method of claim 2,
The second amine is oleyl amine (OLA; oleylamine) the FeS ₂ nanocrystals shape (shape) is characterized in that the sphere (spherical), FeS ₂ nanocrystals method if they include. 3. The method of claim 2,
The FeS ₂ nanocrystals shape (shape) are, FeS, characterized in that the cuboid (cubic) ₂ nanocrystals method if they include; (Trioctylamine TOA) the second amine is trioctylamine. Fe-surfactant precursor solutions were prepared by mixing FeCl ₂ .4H ₂ O (Iron (II) chloride tetrahydrate), octadecylamine (ODA) and trioctylamine (TOA) Preparing;
Preparing sulfur-precursor solution by mixing sulfur with oleylamine (OLA) or trioctylamine (TOA);
Injecting the sulfur-precursor solution into the iron-surfactant precursor solution, heating the solution, and stirring the solution in a nitrogen atmosphere at a heating temperature to grow FeS ₂ nanocrystals; And
Cooling the FeS ₂ nanocrystal mixed solution and purifying FeS ₂ nanocrystals by precipitation reaction with chloroform;
, ≪ / RTI &
The purity of the FeS ₂ nanocrystals is controlled by controlling the amount of the octadecylamine (ODA), and when the sulfur-precursor solution contains oleylamine (OLA), the FeS ₂ nanocrystals have a shape when the shape of the FeS ₂ nanocrystal is spherical rather than cubic and the solution of sulfur-precursor includes trioctylamine (TOA), the FeS ₂ nanocrystal has a spherical shape, Wherein the FeS ₂ nanocrystal is cubic.

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