Preparation and properties of titanium trisulfide nanoparticles

Article abstract of DOI:10.1134/S0022476617050250

Stable colloidal dispersions with a 2 mM TiS₃ concentration (300 mg/l) are obtained by ultrasonic treatment of TiS₃ in acetonitrile and isopropyl alcohol and characterized by physicochemical methods. The electrical double layers for the particles in dispersions are estimated from the measured ζ-potentials, and the energies of interparticle interactions are calculated based on the Derjaguin–Landau–Verwey–Overbeek theory. The structural and spectroscopic identity of the particles and crystalline TiS₃ is demonstrated for the solid phases obtained from the dispersions.

Full text of DOI:10.1134/S0022476617050250

Journal of Structural Chemistry. Vol. 58, No. 5, pp. 1033-1038, 2017.
Original Russian Text © 2017 I. P. A. Poltarak, A. A. Poltarak, S. B. Artemkina, T. Yu. Podlipskaya, V. E. Fedorov.
PREPARATION AND PROPERTIES OF TITANIUM
TRISULFIDE NANOPARTICLES
1,2 1,2
P. A. Poltarak , A. A. Poltarak ,
UDC 546.824:549.32/.33
1 1
S. B. Artemkina *, T. Yu. Podlipskaya ,
1,2
and V. E. Fedorov
Stable colloidal dispersions with a 2 mM TiS3 concentration (300 mg/l) are obtained by ultrasonic treatment
of TiS3 in acetonitrile and isopropyl alcohol and characterized by physicochemical methods. The electrical
double layers for the particles in dispersions are estimated from the measured ζ-potentials, and the energies
of interparticle interactions are calculated based on the Derjaguin–Landau–Verwey–Overbeek theory. The
structural and spectroscopic identity of the particles and crystalline TiS3 is demonstrated for the solid
phases obtained from the dispersions.
DOI: 10.1134/S0022476617050250
Keywords: layered compounds, titanium trisulfide, colloidal dispersion, ultrasonic dispersing, titanium
trisulfide nanoparticles, photon correlation spectroscopy, hydrodynamic diameter, transmission electron
microscopy.
INTRODUCTION
The first publications on graphene [1] and exfoliation of transition metal dichalcogenides [2] gave rise to
considerable interest in the study of other layered materials, particularly nanosized samples. One of the promising ways to
obtain nanoparticles is the dispersing of compact crystalline samples with the formation of colloidal dispersions. This
approach has been successfully applied to the compounds with layered structures, for example, multilayered graphene
materials, transition metal dichalcogenides MQ2 (M = Ti, Zr, Hf; V, Nb, Ta; Mo, W; Q = S, Se), and others. In our work we
consider another large family of transition metal trichalcogenides, which can be structurally attributed to layered systems.
According to the structural and spectroscopic data, trichalcogenides MQ3 (M = Ti, Zr, Hf, Nb, Ta, U; Q = S, Se, Te) can be
4+
2– 2–
2–
2–
described by an ionic model M (Q2) Q [3] containing chalcogenide ions Q and dichalcogenide groups (Q2) . Although
the {MQ6/2} prism is a basic structural unit for MQ2 and MQ3, transition metal trichalcogenides have more complex crystal
structures. Non-equivalence of chalcogen atoms in MQ3 results in the formation of distorted (wedge-shaped) prisms, where
2–
shortened Q–Q bonds point at the dichalcogenide groups (Q2) . These prisms with M atoms inside (located close to the
center of the prisms) share triangular bases and form infinite columns oriented along the b direction (Fig. 1a). Due to short
M…Q contacts between the neighboring columns, polymer layers form whose surfaces are formed by dichalcogenide groups
2–
(Q2) (Fig. 1b). Therefore, transition metal trichalcogenides MQ3 can be considered as layered compounds together with
dichalcogenides MQ2.
1
Nikolaev Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia;
2
*artem@niic.nsc.ru. Novosibirsk National Research State University, Russia. Translated from Zhurnal Strukturnoi Khimii,
Vol. 58, No. 5, pp. 1072-1077, June-July, 2017. Original article submitted December 28, 2016.
0022-4766/17/5805-1033 © 2017 by Pleiades Publishing, Ltd.
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Fig. 1. Two wedge-shaped columns (a) and the
packing of polymer layers in the crystal structure
of TiS3 (b).
The crystal structure of monoclinic TiS3 belongs to the ZrSe3 structure type, which has one type of wedge-shaped
0
columns [4, 5]. In the approximation of the ionic model, titanium in TiS3 has the d electronic configuration, and this
compound is a diamagnetic semiconductor. The quantum chemical modeling of the electronic structure of TiS3 [6] gives the
band gap in a range of 0.48-2.17 eV; the calculated optical absorption spectra show the onset of light absorption within 0.9-
1.5 eV suggesting its possible use in photovoltaics and photocatalysis.
By optical methods it is established that on passing from crystalline TiS3 to nanolayers the second direct optical
transition appears: Eg1 = 1.0 0.1 eV and Eg2 = 1.4 0.1 eV [7]. The investigation of TiS3 nanoribbons revealed interesting
physical properties. A thin TiS3 particle (with a thickness of several crystallographic layers) exhibits planar anisotropy of the
electroconductivity. Under room conditions the anisotropy is 2.1 [8] (for example, cf. with 1.8 for black phosphorus [9]). In
another research, TiS3 nanoribbons were used as an anode in the hydrogen reaction. The efficiency of hydrogen
photogeneration was 7% [10]. For these experiments TiS3 nanocrystals were used.
We have recently reported the studies on obtaining NbS3, NbSe3, TaS3 nanoparticles [11-13]. Indeed, during
ultrasonic treatment trichalcogenides, which are deemed to have layered structures, exfoliated and formed thin nanoparticles
with a diameter of hundreds of nanometers and a thickness of 2-20 nm. In this work, with the aim to prepare TiS3 powders
and other materials containing TiS3 with large surface areas, we obtained colloidal dispersions of TiS3 in liquid media under
ultrasonic effect. The TiS3 particles in these colloidal dispersions and some properties of these colloidal dispersions are
discussed.
EXPERIMENTAL
Methods and equipment. Powder X-ray diffraction (XRD) patterns were recorded on a Philips PW 1830/1710
diffractometer (CuK radiation, graphite monochromator; silicon slab was the external standard). Raman spectra were
α
recorded on a Triplemate spectrometer (laser wavelength of 488 nm). The electronic absorption spectra (EAS) were recorded
on an Agilent Cary 60 spectrometer in a wavelength range from 200 nm to 1100 nm.
Particle sizes were measured by photon correlation spectroscopy (PCS) on a NanoBrook Omni spectrometer
(Brookhaven, USA) in glass cuvettes (1 cm) at 20 °C. The photon accumulation time per measurement was 10 s. The solid
state laser power with an emission wavelength of 640 nm was 35 mW; a detector was located at an angle of 90° to the laser
radiation source. The medium z-averaged (over intensities) hydrodynamic diameter Dh was calculated by the Stokes–Einstein
formula [14] for spherical particles as a mean of 25-30 measurements. The method error did not exceed 5%.
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The electrophoretic mobility of particles and the conductivity of colloidal dispersions were measured on a Zetasizer
Nano ZS device (Malvern Instr.). Three parallel measurements were taken for each dispersion. Electrokinetic potentials were
calculated by the Smoluchowski formula.
Transmission electron microscopy (TEM) images of the particles were obtained on a JEM 4000EX microscope with
an accelerating voltage of 400 kV. The dispersing was carried out in Sapfir ultrasonic baths (power 130 W). The resulting
dispersions were centrifuged on an Eppendorf 5430 centrifuge in 50 ml tubes.
Synthesis of TiS3. 6.991 g (0.2181 mol) of crystalline sulfur and 3.323 g (0.06942 mol) of titanium powder were
placed in a quartz ampoule (volume 45 ml). A sulfur excess is required to prevent the decomposition of titanium trisulfide
into disulfide and sulfur. The ampoule was evacuated, sealed, and placed in a furnace. The synthesis was performed at
a temperature of 500 °C for 150 h. The resulting product was washed from the sulfur excess with toluene in a Soxhlet
extractor.
Preparation of colloidal dispersions of TiS3. Titanium trisulfide TiS3 (100 mg) was placed in 100 ml of an organic
medium and subjected to ultrasonic treatment at 60% of the bath power for 40 h. Acetonitrile (CH3CN), ethanol, dimethyl
formamide (DMF), isopropanol (i-PrOH), n-methylpyrrolidone, and dimethyl sulfoxide (DMSO) were used as the dispersion
media. After ultrasonic treatment all colloidal solutions were centrifuged (2000 rps, 500 g, 10 min). Then we dealt with
dispersions in acetonitrile and isopropanol because they did not coagulate for at least a week.
Determination of the concentration of colloidal dispersions. An aliquot of the dispersion was passed through
a Whatman Anodisc filter (pore size of 0.02 µm). The obtained filter with a layer of the solid phase from the colloidal
dispersion was dried in a drying furnace at 80 °C for 2 h. The TiS3 content in the solutions was calculated from the mass
difference before and after filtering.
RESULTS AND DISCUSSION
Initial TiS3. TiS3 prepared is a dark gray crystalline solid product resembling a sponge due to a large number of
needle-shaped crystals. All reflections observed in the powder XRD pattern belong to the structure of titanium trisulfide
determined previously in [5] (ICSD No 42-072); no other reflections were found. The lines in the Raman spectrum
correspond to the vibrational modes of the TiS3 lattice [15]. Thus, it can be concluded that the product synthesized is pure
titanium trisulfide.
Colloidal dispersions of TiS3. Ultrasonication experiments on TiS3 in different media showed that TiS3 was well
dispersed in acetonitrile and isopropanol forming stable (over 7 days) gray dispersions. The dispersions in acetonitrile and
isopropanol contained 390 mg/l (2.7 mM TiS3 formula units) and 260 mg/l (1.8 mM TiS3) respectively. Ultrasonic treatment
of TiS3 in other media (DMSO, DMF, ethanol, and n-methylpyrrolidone) did not result in the formation of stable colloidal
dispersions.
In EAS (Fig. 2) a characteristic increase in the degree of absorption with decreasing wavelength explained by
Rayleigh scattering on colloidal particles can be observed. EAS of the TiS3 colloidal dispersions in general repeat each other;
the absorption bands are at 950 nm, 640 nm, 400 nm, and 280 nm.
In the TEM images (Fig. 3a) it is seen that the main part of the particles are elongated plates whose lateral
dimensions strongly vary in a range from tens of nanometers to units of microns. Electron diffraction on one TiS3 particle
(Fig. 3b; the particle image is shown in the inset) was indexed in the space group P21/m; the extinctions characteristic of this
symmetry group were observed in the image (the observability conditions of reflections 0k0: k = 2n). Hence, we can conclude
that the particles in colloidal solutions are crystalline. The TEM images indicate the presence of an amorphized layer on the
surface of TiS3 particles; for the particles in the isopropanol dispersion its thickness is 5-10 nm.
Results of the PCS study of the particle size in TiS3 dispersions and their electrokinetic potential are given in
Table 1. The obtained data were used to estimate the stability of TiS3 dispersions in acetonitrile and isopropyl alcohol
following the Derjaguin–Landau–Verwey–Overbeek theory (DLVO theory [16]).
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Fig. 2. Electronic absorption spectra of the
TiS3 colloidal dispersions in acetonitrile (1)
and isopropanol (2).
Fig. 3. Images (TEM) of the TiS3 particles obtained by ultrasonic
dispersing in isopropanol (a). Electron diffraction on the TiS3 particle
(b) and its image in the inset.
TABLE 1. Average Hydrodynamic Diameters (Dh), Electrokinetic Potentials (ζ), Electroconductivity (σ) and the Calculated
Electrical Double Layers (δ) of the Particles in the TiS3 Colloidal Dispersions
Dh, nm
C, mol/l
Observed stability
Medium (ε at 25 °C)
ζ, mV
σ, mS/cm
δ, nm
–4
CH3CN (38.0)
174
234
–30.1
–60.0
0.01292
0.00679
20.2
19.3
Good
Good
1.10⋅10
–5
iPrOH (18.3)
5.80⋅10
According to the DLVO theory, it is possible to calculate the potential barrier height (or the potential well depth)
and estimate the stability of the obtained dispersions from the electrokinetic potential, electroconductivity, particle sizes and
shapes. As evident from Table 1, in both solvents the nanoparticles carry a negative surface charge, but its origin is not
known.
The interparticle interactions were calculated using the DLVO theory for spherical particles with the sizes equal to
the effective hydrodynamic diameters. The formulas required for the calculations and the assumptions made were taken from
our previous study of NbS2 particles [11].
Fig. 4 shows the calculated electrostatic, van der Waals, and total energies of interparticle interactions of TiS3
particles depending on the distance l between them for the dispersions in acetonitrile and isopropyl alcohol. For both systems,
large values of potential barrier height were obtained: 17kT (lmax = 6 nm) for the dispersion in acetonitrile and 50kT
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Fig. 4. Electrostatic (1), van der Waals (2), and total (3) energies of interparticle interactions
depending on the distance l between the spherical particles for the TiS3 dispersions in isopropyl
alcohol (a) and acetonitrile (b).
(lmax = 5 nm) for the dispersion in isopropanol. Note that the DLVO theory estimates agree well with the visually observed
stability of the dispersions.
The precipitates from the colloidal dispersions of TiS3 were analyzed using powder XRD and Raman scattering. All
reflections observed (Fig. 5) belong to titanium trisulfide phases. For the precipitate obtained from the isopropanol dispersion
an increase in the 00l reflection intensity was observed as compared to other reflections, which can be explained by a high
degree of texturization since the particles in the 00l crystallographic direction are mainly oriented parallel to the filter plane.
This effect was not observed for the acetonitrile dispersion.
The positions of vibrational bands in the Raman spectra of dispersed TiS3 correspond to the vibrational bands of
crystalline samples, the appearance of new bands or a change in the shape of the existing ones being not observed. The
–1
vibrational bands in the spectra are in the following positions (in parentheses the data are given from [15]): A 174 (175 cm ),
g
–1
–1
–1
–1
A 296 (300 cm ), A , B 367 (366 cm and 370 nm ), A 554 (557 cm ). The powder XRD and Raman spectral data allow
g
g
g
g
us to conclude that during the ultrasonic dispersing in acetonitrile and isopropanol the TiS3 structure remains unchanged.
Thus, the work shows that TiS3 particles in the form of micronanoribbons can be obtained by ultrasonic treatment of
crystalline TiS3 in acetonitrile and isopropanol, with the TiS3 content in the colloidal dispersion being ≈2 mM. The TiS3
Fig. 5. Powder XRD patterns of the particles deposited on the filter from the TiS3 colloidal solutions in
isopropanol (1) and acetonitrile (2), and of crystalline TiS3 (3). The filter reflections are denoted by asterisks
(a). The Raman spectra of the TiS3 precipitates from the colloidal dispersions in isopropanol (1) and
acetonitrile (2) and of initial TiS3 (3) (b).
1037

dispersions are the matrices with a large surface area and are stable for more than one week. This can be useful for the
preparation of different composites for photocatalysis and other applications.
The work was supported by RFBR (RFBR grant No. 16-33-00577mol_a).
The authors are grateful to D-r I. A. Pyshnaya (Institute of Chemical Biology and Fundamental Medicine, Siberian
Branch of the RAS) for measurement of the electrokinetic potentials.
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