Publications
2020
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(2020) Physics Today. 73, 8, p. 42-48 Abstract
The two-dimensional materials form one- and zero-dimensional hollow structures with a host of promising mechanical, optical, and electrical properties.
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(2020) Applied Materials Today. 19, 100581. Abstract
The non-stoichiometric misfit layered compounds (MLC) of the general formula ((MX)(1+y))(m)(TX2)(n) (abbreviated herein as MX-TX2) have been investigated quite extensively over the last 30 years. Here MX is a atomic slab of a material with distorted rocksalt structure and TX2 is a layered compound with hexagonal (octahedral) coordination between the metal T atom and the chalcogen X atom. Recognizing the mismatch between the two (MX and TX2) sublattices, nanotubes from the MLC of different compositions were described in the past. In particular, semimetallic nanotubes belonging to the family LnX-TaX2 with Ln = rare earth atom and X = S, Se, Te have been studied in the past. While some of them, like LaS-TaS2 were obtained with moderately high yields, others like YbS-TaS2 were scarce. In the present study, a new strategy for promoting the yield of such MLC nanotubes by alloying the LaS sublattice with another Ln atom is proposed. Detailed transmission electron microscopy investigation of the (mixed) Ln(x)La((1-x))S-TaS2 (Ln = Pr, Sm, Ho, Yb) nanotubes show clearly that the substituting Ln atom resides in the rocksalt LaS sublattice of the nanotubes. Raman measurements show distinct differences between mixed tubes with open-shell (Pr, Sm, Ho) and close-shell (La, Yb) rare-earth atoms. Density functional calculations show that the interplay between two important factors determine the enhanced stability of the mixed nanotubes- the size and electronic structure of the substituting rare-earth atom. The smaller is the substituting rare-earth atom (larger Z number), the more dissimilar it is to the original La atom. This dissimilarity enhances the incommensurability between the Ln(x)La((1-x))5 and the TS2 subunits, promoting thereby the stability of the mixed MLC. However, the electronic structure of the Ln atom was found to play a more significant role. The MLC lattice of the LaS-TaS2 is electron-rich and consequently the 4d(z)(2) level of Ta is full. The unoccupied 4f levels of the substituent open-shell atoms (Pr, Sm, Ho), which are positioned below the Fermi level, serve as electron acceptors. Consequently, the Ln substitution is found to enhance the stability of the mixed lattice and nanotubes thereof. This strategy can be employed for enhancing the yield of these and other misfit nanotubes using different substituents of the right size and energy profile.
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(2020) Crystals. 10, 6, 468. Abstract
Misfit layered compounds (MLCs) have been studied in the literature for the last 40 years. They are generally made of an alternating sequence of two monolayers, a distorted rocksalt structure, and a hexagonal layered compound. In a typical MLC, the c-axis is common to the two monolayers and so is one of the axes in the layer plan. However, the two compounds are non-commensurate along at least one axis, and the ratio between the two axes is an irrational number making the MLC a non-stoichiometric compound. The two main families of MLC are those based on metal dichalcogenides and CoO2 as the hexagonal layered compound. Traditionally, ternary MLCs were prepared and studied, but some quaternary and multinary MLC minerals have been known for many years. Over the last few years, interest in MLCs with four and even larger number of atoms has grown. Doping or alloying of a ternary MLC permits precise control of the charge carrier density and hence the electrical, thermoelectric, catalytic, and optical properties of such compounds. In this short review, some of these developments will be discussed with the main emphasis put on quaternary MLC nanotubes belonging to the chalcogenide series. The synthesis, structural characterization, and some of their properties are considered. Some recent developments in quaternary cobaltite MLCs and recent studies on exfoliated MLCs are discussed as well.
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(2020) Scientific Reports. 10, 1, 8892. Abstract
WS2 inorganic nanotubes (WS2-NT) have been incorporated into Polylactic Acid (PLA) by melt mixing to create a bio-degradable, mechanically reinforced nanocomposite filament. The filament was then processed by Fused Filament Fabrication (FFF) 3D-printer, and the morphology and characteristics before and after printing were compared. We found that addition of WS2-NT to PLA by extrusion mixing increases the elastic modulus, yield strength and strain-at-failure by 20%, 23% and 35%, respectively. Moreover, we found that the printing process itself improves the dispersion of WS2-NT within the PLA filament, and does not require changing of the printing parameters compared to pure PLA. The results demonstrate the advantage of WS2-NT as reinforcement specifically in 3D-printable polymers, over more traditional nano-reinforcements such as graphene and carbon nanotubes. WS2-NT based 3D-printable nanocomposites can be used for variety of applications from custom-made biodegradable scaffold of soft implants such as cartilage-based organs and biodegradable soft stents to the more general easy-to-apply nano-reinforced polymers.
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(2020) Journal of Materials Science. 55, 18, p. 7612-7623 Abstract[All authors]
Due to their high porosity, aerogels can be efficiently used as host matrices for functional materials. The solid matrix is advantageous over liquid suspensions because it maintains the nanoparticles static and inhibits agglomeration and precipitation. The current paper reports on the controlled addition of less than 0.1 wt% of WS2 nanotubes (WS2 NTs) to aerogels, retaining the aerogel's mesoporous structure, and demonstrates how increasing nanotubes' concentration influences the optical properties of the composite aerogel. The absorption spectrum of WS2 NTs consists of two peaks, attributed to the direct gap transition and referred to as excitons A and B and is preserved in the aerogel. WS2 NTs' extinction spectrum, on the other hand, is dominated by exciton-polaritons and is modified in the aerogel, with respect to the NTs dispersed in liquid. This occurs due to scattering effects, resulting in broadening with increased NT content, washing out the excitonic transitions. Furthermore, femtosecond optical pump-probe measurements carried out on NTs dispersed in both ethanol and the silica aerogel suggest that the electronic processes underlying the overall optical behaviour of the nanotubes, and hence also their optoelectronic and photochemical properties are preserved in the aerogel matrix. These findings make the obtained nanocomposites interesting for use in modern optical and optoelectronic devices.
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(2020) ACS Nano. 14, 5, p. 5445-5458 Abstract
We present the analysis of a family of nanotubes (NTs) based on the quaternary misfit layered compound (MLC) YxLa1-xS-TaS2. The NTs were successfully synthesized within the whole range of possible compositions via the chemical vapor transport technique. In-depth analysis of the NTs using electron microscopy and spectroscopy proves the in-phase (partial) substitution of La by Y in the (La,Y)S subsystem and reveals structural changes compared to the previously reported LaS-TaS2 MLC-NTs. The observed structure can be linked to the slightly different lattice parameters of LaS and YS. Raman spectroscopy and infrared transmission measurements reveal the tunability of the plasmonic and vibrational properties. Density-functional theory calculations showed that the YxLa1-xS-TaS2 MLCs are stable in all compositions. Moreover, the calculations indicated that substitution of La by Sc atoms is electronically not favorable, which explains our failed attempt to synthesize these MLC and NTs thereof.
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(2020) ACS Applied Energy Materials. 3, 5, p. 4619-4628 Abstract[All authors]
Proton exchange membranes with high through-plane proton conductivity are a critical component of high-performance fuel cells, electrolyzers, and batteries. However, isotropically distributed proton-conducting channel structures of current membranes present a limitation. Herein, a proton exchange membrane with straight proton-conducting channels aligned in the thickness direction is fabricated, achieved by magnetic field-induced alignment of proton-conductive, paramagnetic, and one-dimensional (1D) tungsten disulfide nanotubes (pms-WS2) distributed in a perfluorinated sulfonic acid (Nafion) membrane. The pms-WS2 nanotubes feature straight WS2 nanotubes as a core, a polystyrenesulfonate (PSS) skin layer, and surface-decorated Fe3O4 nanoparticles. A molecular dynamics simulation suggests that straight proton-conducting channels are constructed at the interface of Nafion/pms-WS2 due to densely populated sulfonic acids. Spectroscopic investigation and magnetization measurements verify the through-plane alignment of pms-WS2 under a weak through-plane magnetic field (0.035 T) during the removal of solvent from the membrane cast. Compared with a recast Nafion membrane with the same thickness, the through-plane aligned composite membrane exhibits 69% higher proton conductivity and 51% higher power performance in a proton exchange membrane fuel cell, demonstrating its efficacy. The through-plane alignment of a proton-conductive inorganic 1D material promises improved power performance of advanced electrochemical devices.
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(2020) ACS Energy Letters. 5, 5, p. 1498-1511 Abstract
The global impact of carbonaceous emissions from the internal combustion engine and coal-fired power plants has stimulated efforts to mitigate global warming and deterioration of the habitable biosphere. These efforts resulted in the maturation of new technologies to harvest and store the natural energies available-wind, waves, geothermal, sun and outer space radiation - for conservation and security. Inorganic layered compounds (2D materials), like MoS2, TiS2 and CoO2 played a major role in the upbringing of novel energy technologies, which can one day replace fossil fuel in the transport industry as well as in other energy-consuming sectors. In this perspective, the history of various concepts explored in energy-related research using bulk layered compounds (2D materials), is briefly reviewed, first. The recent addition of 2D nanostructures, in energy conversion and storage, has added significant momentum to this research field. Particularly, this perspective places a great emphasis on the study of inorganic fullerene-like nanoparticles and nanotubes from 2D materials, and to some extent also on the atomically thin single layer solids, that apparently surpasses the performance of other respective allotropes in the pursuit of their use in energy storage/conversion, catalysis, and sensing.
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(2020) Zhidkie Kristally i Ikh Prakticheskoe Ispol'zovanie. 20, 1, p. 34-40 Abstract
Time parameters (reaction time and relaxation time of medium) of liquid crystal cell sensitized with WS2 nanoparticles and constructed taking into account the modification of the conductive ITO coating by carbon nanotubes are considered. Carbon nanotubes were vertically deposited on the surface of the conductive layer using the laser method and the orientation effect of an electric field with a strength of 600 V/cm. The use of two control functions, namely: the sensitization process of mesophase volume and nanostructuring of the solid - liquid crystal interface allowed increasing the mesophase switching performance and significantly reducing the resistance of the conductive layers acted as orientant and conductor.
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(2020) Small. 16, 4, 1904390. Abstract
Multiwall WS2 nanotubes (and fullerene-like nanoparticles thereof) are currently synthesized in large amounts, reproducibly. Other than showing interesting mechanical and tribological properties, which offer them a myriad of applications, they are recently shown to exhibit remarkable optical and electrical properties, including quasi-1D superconductivity, electroluminescence, and a strong bulk photovoltaic effect. Here, it is shown that, using a simple dispersion-fractionation technique, one can control the diameter of the nanotubes and move from pure excitonic to polaritonic features. While nanotubes of an average diameter >80 nm can support cavity modes and scatter light effectively via a strong coupling mechanism, the extinction of nanotubes with smaller diameter consists of pure absorption. The experimental work is complemented by finite-difference time-domain simulations, which shed new light on the cavity mode-exciton interaction in 2D materials. Furthermore, transient absorption experiments of the size-fractionated nanotubes fully confirm the steady-state observations. Moreover, it is shown that the tools developed here are useful for size control of the nanotubes, e.g., in manufacturing environment. The tunability of the light-matter interaction of such nanotubes offers them intriguing applications such as polaritonic devices, in photocatalysis, and for multispectral sensors.
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(2020) Zhidkie Kristally i Ikh Prakticheskoe Ispol'zovanie. 20, 3, p. 41-48 Abstract
Based on the analysis of spectral parameters, orientation angle, and the time dependency of the reaction and relaxation of the media composed of the nematic liquid crystal mesophase and WS2 nanoparticles, the correlation associated with the formation of intermolecular interaction between CN-group of the liquid crystal and WS2 nanoparticle has been established. The correlation was supported by experiments and partially by quantumchemical modeling.