Centrum pre Nanodiagnostiku Materiálov

Fahimeh Gholami, Arash Ghazitabar, Malek Naderi, Aylar Hoviatdoost, Delasa Ali Jani Ashna, Kiarash Ghazitabar, Bogumił Brycki, Viliam Vretenár

In: Surfaces and Interfaces, (2024)

https://doi.org/10.1016/j.surfin.2024.103936

Abstract

In this study, N-doped cobalt-decorated graphene/carbon nanotube/cellulose microfiber composite aerogels were synthesised and used as oil sorbent. In the current approach, graphene aerogel nanocomposites containing carbon nanotubes and cellulose microfibres were synthesised through a chemical reduction process using ascorbic acid and sodium bisulphite as reducing agents. Subsequently, N-doping was performed using ammonium treatment. The microstructure of these composites was characterised by field emission and conventional scanning electron microscopy, and transmission electron microscopy measurements. The molecular bonding and composition of the composites were analysed using energy-dispersive spectroscopy, Fourier Transform Infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The hydrophobicity of the composites was characterised by a water contact angle test. Finally, the oil sorption performance of the samples was evaluated through a self-design procedure based on a combination of ASTM F716 and 726 standards and Bazargan et al. report. The N-doped Co decorated graphene/carbon nanotube/cellulose microfiber sample with a GO:CNT:CMF mass ratio of 4:2:1 (CGCMF-24) demonstrated the highest hydrophobicity and oil sorption capacity in comparison with other samples. CGCMF-24 adsorbed up to 30, 44, and 54 g/g toluene, cyclohexane, and hexane, respectively. Meanwhile, the most durable adsorbent was CGCMF-24, with 74% durability after five sorption-desorption cycles, and it maintained this capacity for up to 10 cycles.

Filip Zechel, Peter Hutár, Viliam Vretenár, Karol Végsö, Peter Šiffalovič, and Milan Sýkora

In: Inorg. Chem. 2023, 62, 40, 16554–16563

https://doi.org/10.1021/acs.inorgchem.3c02420

Abstract

Currently, two approaches dominate the large-scale production of MoS2: liquid-phase exfoliation, referred to as the top-down approach, and bottom-up colloidal synthesis from molecular precursors. Known colloidal synthesis approaches utilize toxic precursors. Here, an alternative green route for the bottom-up synthesis of MoS2 nanoflakes (NFs) is described. The NFs were synthesized by colloidal synthesis using [Mo(CH3COO)2]2 and a series of sulfur (S)-precursors including thioacetamide (TAA), 3-mercaptopropionic acid (3-MPA), l-cysteine (L-CYS), mercaptosuccinic acid (MSA), 11-mercaptoundecanoic acid (MUA), 1-dodecanethiol (DDTH), and di-tert-butyl disulfide (DTBD). While TAA, an S-precursor most commonly used for MoS2 NF preparation, is a known carcinogen, the other investigated S-precursors have low or no known toxicity. High-resolution scanning transmission electron microscopy (HR-STEM) and grazing incidence wide-angle X-ray scattering (GIWAXS) confirmed that in all cases, the syntheses yielded single-layer MoS2 NFs with lateral sizes smaller than 15 nm and a well-defined crystal structure. Electronic absorption and Raman spectra showed characteristic features associated with the MoS2 monolayers. The evolution of the absorption spectra of the growth solution during the syntheses reveals how the kinetics of the NF formation is affected by the S-precursor as well as the nature of the coordinating ligands.

PAULAUSKAS, Tadas – ACEECHAVIČIUS, Bronislovas – KARPUS, Vytautas – JOČIONIS, Lukas – TUMĖNAS, Saulius – DEVENSON, Jan – PAČ̌EBUTAS, Vaidas – STANIONYTE, Sandra – STRAZDIENE, Viktorija – GEIAUTIS, Andrejus – ČAPLOVIČOVÁ, Mária – VRETENÁR, Viliam – WALLS, Michael G. – KROTKUS, Arunas

In Journal of Applied Physics. Vol. 128, iss. 19 (2020)

https://doi.org/10.1063/5.0030091

ABSTRACT

The GaAs_1–xBi_x semiconductor alloy allows one to achieve large bandgap reduction and enhanced spin–orbit splitting energy at dilute Bi quantities. The bismide is currently being developed for near- to mid-infrared lasers, multi-junction solar cells, and photodetectors. In this structure–property relationship study of GaAsBi alloys, we report polarization dependent photoluminescence that reaches a polarization ratio up to 2.4 at room temperature. Polarization dependence is also presented using transmittance spectra, birefringence, and linear dichroism. The optical anisotropy observations agree with the predictions of point symmetry reduction in the CuPt_B-type ordered GaAsBi phase. The structural ordering is investigated experimentally from the atomic scale in molecular-beam epitaxy (MBE) grown samples on exact and miscut (001) GaAs substrates, as well as on (001) Ge. The latter sample is composed of anti-phase domains in which the ordering axes are rotated by 90° angles. Since the conditions stabilizing the CuPt_B ordered phase fall within the typical MBE growth regime of dilute bismides, the optical anisotropy in GaAsBi alloys is expected to be ubiquitous. These findings are important for the future development of GaAsBi-based optoelectronics and also provide new means to analyze structurally complex bismide alloys.

PAULAUSKAS, Tadas – PACEBUTAS, Vaidas – GEIZUTIS, Andrejus – STANIONYTE, Sandra – DUDUTIENE, Evelina – SKAPAS, Martynas – NAUJOKAITIS, Arnas – STRAZDIENE, Viktorija – CECHAVICIUS, Bronislovas – ČAPLOVIČOVÁ, Mária – VRETENÁR, Viliam – JAKIELA, Rafal – KROTKUS, Arunas

In Scientific Reports. Vol. 10, iss. 1 (2020)

https://doi.org/10.1038/s41598-020-58812-y

Abstract

The dilute bismide alloy GaAs_1-xBi_x has drawn significant attention from researchers interested in its fundamental properties and the potential for infrared optoelectronics applications. To extend the study of bismides, molecular-beam heteroepitaxy of nominally 1.0 eV bandgap bismide on Ge substrates is comprehensively investigated. Analysis of atomic-resolution anti-phase domain (APD) images in the direct-epitaxy revealed a high-density of Ga vacancies and a reduced Bi content at their boundaries. This likely played a key role in the preferential dissolution of Bi atoms from the APD interiors and Bi spiking in Ge during thermal annealing. Introduction of GaAs buffer on offcut Ge largely suppressed the formation of APDs, producing high-quality bismide with single-variant CuPt_B-type ordered domains as large as 200 nm. Atomic-resolution X-ray imaging showed that 2-dimensional Bi-rich (111) planes contain up to x = 9% Bi. The anomalously early onset of localization found in the temperature-dependent photoluminescence suggests enhanced interactions among Bi states, as compared to non-ordered samples. Growth of large-domain single-variant ordered GaAs_1-xBi_x films provides new prospects for detailed analysis of the structural modulation effects and may allow to further tailor properties of this alloy for optoelectronic applications.

GUARDIA, Laura – SUÁREZ, Loreto – QUEREJETA, Nausika – VRETENÁR, Viliam – KOTRUSZ, Peter – SKÁKALOVÁ, Viera – CENTENO, Teresa A.

In Electrochimica Acta. Vol. 298, iss. 3 (2019)

https://doi.org/10.1016/j.electacta.2018.12.160

Abstract

We present a simple and effective alternative which optimizes electrodes based on low-cost carbons for high-performance supercapacitors. The combination with reduced graphene oxide (rGO) greatly improves the operation of microporous carbons easily produced by one-pot activation of grape seeds. The use of composite electrodes with rGO lowers the supercapacitor resistance and enables a much higher rate capability.

The mixture of rGO flakes and particles of a highly porous carbon obtained by KOH activation allows retaining the high capacitance of 260 F g⁻¹ of the standard electrodes at 1 mA cm⁻² in aqueous H₂SO₄ whereas the value at 200 mA cm⁻² is increased by around 2.4 times. Consequently, at high current density, the capacitor assembled with these composites stores eight times more energy and the power density is multiplied by four.

The synergy between rGO and an ultramicroporous carbon produced by CO₂-activation results extremely profitable, the cell assembled with composite electrodes reaching three times more energy and power at 200 mA cm⁻² than the best performance of the standard counterpart.

More importantly, the higher density of the composite electrodes leads to a capacitance of around 200 F cm⁻³ which translates into a remarkable improvement in the supercapacitor operation normalized to volume.