RU2552451C2 - Method of obtaining nanosized materials - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in the chemical technology. To obtain nanosized and nanostructured materials based on layered trichalcogenides of transition metals of the general formula MQ₃, where M=Ti, Zr, Hf, Nb, Ta; Q=S, Se, Te, as an initial material used are powder-like trichalcogenides, which are dispersed in nanosized particles by ultrasound processing in an organic solvent. The organic solvent id selected from the group 1-cyclohexyl-2-pyrrolidone, dimethylformamide, N-methylpyrrolidone, acetonitrile, ethanol, isopropanol, their mixtures, water solutions and water solutions of the mixtures. The solid phase of trichalcogenides is separated from the formed colloidal dispersions. The said phase can be obtained in the form of thin films.

EFFECT: invention makes it possible to obtain stable colloidal dispersions of particles of trichalcogenides of transition metals for further obtaining materials based on them.

6 cl, 7 dwg, 1 tbl

Description

The invention relates to the field of chemical technology, namely to the production of nanoscale materials, including thin films, based on transition metal trichalcogenides MQ ₃ (M = Ti, Zr, Nb, Ta; Q = S, Se, Te).

Trends in modern industrial development have demanded new materials with previously unattainable properties, in particular especially thin film and bulk materials, which provide progress in the field of electronic industry, medicine and other fields.

As a starting material for the production of such materials, it is customary to use layered compounds that can be cleaved by various methods, for example, intercalation of ions (see P. Joensen, RF Frindt, SR Morrison, Mater. Res. Bull. 1986, 27, 457 [1] ; D. Yang, RF Frindt, J. Phys. Chem. Solids 1996, 57, 1113 [2];

Z.F. Ding, L. Viculis, J. Nakawatase, R.B. Kaner, Adv. Mater. 2001, 13, 797 [3]; H. Matte, A. Gomathi, A.K. Manna, D.J. Late, R. Datta, S.K. Pati, C.N.R. Rao, Angew. Chem. Int. Ed. 2010, 49, 4059 [4]).

However, this method is extremely time-consuming and very sensitive to production conditions; in addition, when using this method, structural deformations may occur in some layered compounds.

Further studies have shown that delamination in organic solvents can be a more promising way of splitting the layered compounds (see WQ Nan, LJ Wu, YM Zhu, K. Watanabe, T. Taniguchi, Appl. Phys. Lett. 2008, 93, 223103 [5 ]; CY Zhi, Y. Bando, CC Tang, H. Kuwahara, D. Golberg, Adv. Mater. 2009, 27, 2889 [6]; Y. Lin, TV Williams, JW Connell, J. Phys. Chem. Lett . 2010, 7, 277 [7]; JH Wamer, MH Rummeli, A. Bachmatiuk, B. Buchner, ACS Nano 2010, 4, 1299 [8]). In particular, in a recent paper by JN Coleman et al., Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials, Science, 2011, v.331, pp.568-571 [9], a method for dispersing chalcogenides with a layered structure of dichalcogenides transition metals MQ ₂ (M = Nb, Ta, Mo, W, Ni; Q = S, Se, Te), Bi ₂ Q ₃ . According to this method, powdered substances are transferred into a colloidal solution by ultrasonic treatment in polar high-boiling organic solvents such as dimethylformamide (DMF) (boiling point 153 ° C), N-methylpyrrolidone (NMP) (boiling point 202 ° C). Another study by RJ Smith et al., Large-Scale Exfoliation of Inorganic Layered Compounds in Aqueous Surfactant Solutions, Adv. Mater., 2011, 23, 3944-3948 [10] the dispersion of layered inorganic materials is proposed to be carried out in aqueous solutions of surface-active substances (surfactants). In an article by KG Zhou, NN Mao, NH Wang, Y Peng, and Hao-Li Zhang, A Mixed-solvent Strategy for Efficient Exfoliation of Inorganic Graphene Analogues, Angew. Chem. Int. Ed., 2011, 50: 10839-10842 [11] shows that molybdenum and tungsten disulfides MoS ₂ and WS ₂ can be dispersed in a mixed ethanol-water solvent in the concentration range of 35-45 volume percent C ₂ H ₅ OH . The advantage of the latter solvents is their lower boiling points compared to DMF or NMP.

A similar approach is described in US patent No. 4996108 [12], in which a film with a thickness of one molecule was obtained by splitting a layered composition based on the formula MX ₂ : Y, where MX ₂ is a layered structure of transition metal dichalcogenides, M is a metal selected from a group comprising niobium, tantalum, molybdenum and tungsten, X is a chalcogen selected from the group comprising sulfur and selenium, and Y is a material located between the MX ₂ layers. This technical solution is selected as a prototype of the claimed invention.

The problem to which the claimed invention is directed, is to expand the range of starting materials to obtain stable colloidal dispersions, to determine the most effective solvents and other physical methods of processing the starting materials, providing nanoscale final materials.

The technical result is achieved by developing a method for producing nanoscale and nanostructured materials based on layered transition metal chalcogenides MQ ₃ , where M = Ti, Zr, Nb, Ta; Q = S, Se, Those, whose main distinguishing feature is that powdered trichalcogenides are used as the starting material, which are dispersed into nanosized particles by ultrasonic treatment in an organic solvent selected from the group 1-cyclohexyl-2-pyrrolidone, dimethylformamide, N -methylpyrrolidone, acetonitrile, ethanol, isopropanol, including mixtures thereof, aqueous solutions and aqueous solutions of mixtures, followed by isolation of trichalcogenides from the solid colloidal dispersions formed. Volumetric samples of the solid phase of trichalcogenides are obtained by coagulation of a colloidal solution: by adding to the dispersion either electrolytes or other solvents in which this phase is not dispersed; the resulting solid phase is isolated by filtration or centrifugation.

It should be noted that for transition metal trichalcogenides, methods for producing colloidal dispersions were not found in sources known to the authors. These compounds are traditionally considered as quasi-one-dimensional metal chains on the basis of a high degree of anisotropy of electronic conductivity, which is significantly higher in the direction of the axis of the metal chains. However, the authors of the invention, analyzing the crystalline structures of metal trichalcogenides of groups 14-15, came to the conclusion that, although the electrophysical properties of these compounds are clearly one-dimensional, it is reasonable to consider their structures from the crystal chemical point of view as layered, in which the chains are tightly connected to each other so that layers are formed with a thickness of two prisms; such layers are connected in a three-dimensional structure only by Van der Waals forces.

Figure 1 shows the structures trihalkogenidov MQ _3: chains trigonal prisms [MQ6 / 2] in NbSe ₃ structures (1.1) and NbS ₃ (1.2); the projections of such chains in the ac plane in the ZrSe ₃ (1.3), NbS ₃ (1.4), TaSe ₃ (1.5), and NbSe ₃ (1.6) structures.

The preparation of colloidal dispersions of MQ ₃ trichalcogenides (M = Ti, Zr, Hf, Nb, Ta; Q = S, Se, Te) requires the use of simple or mixed organic solvents capable of converting transition metal trichalcogenides MQ ₃ into stable colloidal dispersions.

In practical embodiments of the claimed invention trihalkogenidy powdered transition metal MQ ₃ (TiS _3, NbS _3, NbSe _3, TAS _h) was sonicated in selected solvents at room temperature or under heating. The resulting reaction mixture was centrifuged or settled to remove insoluble particles. The resulting colloidal solution was separated from the precipitate and investigated using various analysis methods. The precipitate was drawn into the re-dispersion process in a new portion of the solvent. As a result, colloidal dispersions were obtained for the entire series of transition metal trichalcogenides MQ ₃ (TiS ₃ , NbS ₃ , NbSe ₃ , TaS ₃ ). Niobium trisulfide dispersions were investigated in more detail.

NbS ₃ crystallizing in a triclinic structure. results

dispersion of NbS ₃ in some important solvents

are presented in Table 1.

For other trichalcogenides, the concentrations of their dispersions were also determined:

TiS ₃ / CH ₃ CN 0.278 g / l; 0.0019 M TiS ₃ / DMF 0.112 g / l; 7.8 · 10 ^-4 M TAS ₃ / DMF 0.061 g / l; 2.67 · 10 ^-4 M Tas ₃ / DMSO very low concentration, about 10 ^-6 M TAS ₃ / NMP no variance NbSe ₃ / C ₂ H ₅ OH 0.042 g / l, 1.28 · 10 ^-4 NbSe ₃ / 'PrOH 0.12 g / l, 3.64 · 10 ^-4 M NbSe ₃ / CN ₃ CN very low concentration NbSe ₃ / DMF, acetone no variance

Particle sizes and their distribution in dispersions were determined by dynamic light scattering. These results are shown in Figure 2. Electronic absorption spectra of different dispersions obtained in the experiments are shown in Figure 3.

As can be seen from the data obtained, the electronic absorption spectra for dispersions of different chalcogenides are very different from each other, this reflects the characteristics of individual phases. For example, the NbS ₃ spectrum contains a characteristic band at 594 nm. This feature was used to determine the concentration of the dispersed substance in the colloid. For the NbS ₃ / DMF dispersion, a calibration curve was created "the dependence of the absorption values of the colloidal dispersion at 594 nm on the concentration of the dispersed substance" (see Figure 4). These data are in good agreement with the data obtained by weighing films obtained by filtering dispersions. This dependence is well approximated by the well-known Lambert-Baire law.

The curves thus obtained for dispersions from other trichalcogenides can also be used to determine the concentration of a dispersed substance in a colloidal solution.

To confirm the individuality of the phases of trichalcogenides in colloidal dispersions, films were prepared by filtering these colloidal dispersions under vacuum. The resulting films were thoroughly characterized by powder diffractometry and Raman spectroscopy.

Thin films of nanoscale trichalcogenides in practical embodiments of the proposed method were obtained by

- vacuum filtration of colloidal dispersions through a Whatman anodisc membrane filter with a pore size of 0.02 μm. Films prepared by this method were dried at 70 ° C in an oven in an air atmosphere;

- spraying colloidal dispersions onto a substrate (spray method) This method involved spraying a colloidal dispersion onto heated (temperature ~ 200-250 ° C) surfaces.

The spray method is technologically more flexible. Using the spray method, it is possible to obtain coatings of complex compositions on various surfaces of complex geometry.

The typical appearance of the films filtered on a Whatman anodisc filter is shown in FIG. 5, where views 51 and 52 are photographs of NbS ₃ films prepared by filtering on a Whatman anodisc (membrane diameter 25 mm, pore size 0.02 μm ); 53 -structure form obtained by filtration NbS film ₃ 0.5 mm thick (with an optical microscope photo); view 54 — structure of the NbS ₃ film obtained by the spray method (photo with an optical microscope).

To confirm the identity of the phase of the trichalcogenide MQ ₃ in the colloidal dispersion, these dispersions were filtered, and the resulting films were carefully characterized by X-ray powder diffraction and Raman spectroscopy. Powder diffraction data of the obtained films are shown in Figure 6, where the form 61 - powder diffraction patterns for different samples NbS ₃ (Film ₃ NbS prepared from a colloidal solution in acetonitrile); view 62 — powder X-ray diffraction patterns for different samples of NbS ₃ (the NbS ₃ film was prepared from a colloidal solution in ethanol); form 63 - powder diffraction patterns for different samples ₃ TAS (TAS _of film prepared from a colloidal solution in dimethylformamide).

As can be seen from the data of powder diffractometry, the solid phases isolated from these dispersions are actually trichalcogenides of the corresponding metals. The diffraction patterns of the films show a noticeable texturing of the material. This is not surprising, since nanoparticles in colloidal solutions have the form of thin plates, which are laid on a plane in a regular way.

Raman spectra of the powders of trichalcogenides and films of trichalcogenides repeat each other, which confirms the individuality of the phases in the films (see Fig.7).

Thus, the totality of the data of various physical methods shows that upon formation of colloidal dispersions, trichalcogenides of transition metals МQ ₃ retain their individuality and can be isolated from solution in the form of nanoscale particles with characteristic sizes of 150-350 nm, from which thin films or coatings of various sizes can be formed forms.

The invention can be most effectively used to produce nanoscale chalcogenide materials containing particles of a size of 150-350 nm, including thin films, coatings and a wide range of composite materials, including multilayer composites with alternating layers of metal, semiconductor and dielectric types, to create film electrodes, thermoelectric and sensor devices, catalysts and other functional nanomaterials. The use of the proposed method allows you to:

- apply powders of trichalcogenides of transition metals MQ ₃ synthesized by solid-phase reaction methods to obtain colloidal dispersions without prior processing;

- use commercial dimethylformamide, N-methylpyrrolidone, acetonitrile, ethanol, isopropanol without distillation or further purification as organic solvents for colloidal dispersions;

- vary both the amount of soluble chalcogenide and the average particle size by selecting the nature of the organic solvent;

for example, in DMF the concentration of niobium trisulfide is 0.059 g / l, and in a mixed ethanol-water solvent the concentration reaches 0.443 g / l; on the other hand, the average particle size of niobium trislenide varies from 110 nm in isopropanol to 450 nm in a mixture of ethanol-dimethylformamide;

- to obtain thin (from 0.25 to tens of microns) films of trichalcogenides by filtering their dispersions through thin membrane filters, as well as to obtain multilayer composites by sequential filtering of various dispersions;

- to obtain thin (including less than micron) films and structures of trichalcogenides, including the preparation of coatings on complex surfaces using the spray method.

Table 1 The formation of colloidal dispersions of NbS ₃ in various solvents Solvent Result (concentrations are indicated according to weighing data and electronic absorption spectra of colloidal dispersions) DMF Stable dispersion C = 0.0589 g / l, 0000312M Acetone NbS ₃ does not disperse Acetonitrile Very good dispersion C = 0.191 g / l, 0.001 M Water No variance Ethanol No variance Water / Ethanol (55/45 vol%) Stable dispersion C = 0.443 g / l, 0.0023 M Isopropyl alcohol Stable dispersion C = 0.332 g / l, 0.0018 M 1-methyl-2-pyrrolidone (NMP) Dispersion is unstable

Claims (6)

1. A method for producing nano-size and nano-structured materials based on transition metal layered trihalkogenidov MQ _3, where M = Ti, Zr, Hf, Nb, Ta; Q = S, Se, Those, characterized in that the starting material uses powdered trichalcogenides which are dispersed into nanosized particles by ultrasonic treatment in an organic solvent selected from the group 1-cyclohexyl-2-pyrrolidone, dimethylformamide, N-methylpyrrolidone, acetonitrile , ethanol, isopropanol, including mixtures thereof, aqueous solutions and aqueous solutions of mixtures, followed by isolation of trichalcogenides from the solid colloidal dispersions formed. 2. The method according to p. 1, characterized in that the powdered trichalcogenides of transition metals are dispersed in mixed or simple solvents. 3. The method according to any one of paragraphs. 1, 2, characterized in that the initially insoluble solid phase of trichalcogenides is involved in the repeated dispersion process in a new portion of the solvent. 4. The method according to p. 1, characterized in that the solid phase of trichalcogenides is obtained in the form of thin films. 5. The method according to p. 4, characterized in that the production of thin films is carried out by vacuum filtration through a membrane filter. 6. The method according to p. 4, characterized in that the production of thin films is carried out by spraying colloidal dispersions on a substrate.

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