• Quantification of alloy atomic composition sites in 2D ternary MoS2(1-x)Se2x and their role in persistent photoconductivity, enhanced photoresponse and photo-electrocatalysis

    Ravi K. Biroju, Dipak Maity, Viliam Vretenár, Ľubomír Vančo, Rahul Sharma, Mihir Ranjan Sahoo, Jitendra Kumar, G. Gayathri, Tharangattu N. Narayanan, Saroj Kumar Nayak

    In: Materials Today Advances, Volume 22, 2024, 100504


    Engineering transition metal dichalcogenides-based semiconducting two-dimensional (2D) layered materials for photo(electro)chemical (PEC) hydrogen evolution reaction (HER) by water splitting is an enduring challenge. Here, alloy-assisted photoconductivity and photoresponse from CVD-grown MoS2(1-x)Se2x (MSSE) 2D ternary atomic layered alloy-based photodetector device is presented for the realization of PEC HER. The explicit role of ‘S–Se’ and ‘Se2’ atomic alloy sites including chalcogen-induced vacancy defects on the photoconductivity/photoresponse and PEC HER performance of MSSE 2D alloy is investigated. Alloy formation, atomic site-by-site ‘Se’ composition and atomic structure are characterized using Raman/Photoluminescence (PL) spectroscopy, high-angle annular dark field (HAADF)- scanning transmission electron microscopy (STEM) extensively and supported with Auger Electron Spectroscopy (AES) mapping. Further, the local density and concentration of S–Se, Se2 atomic sites and defects were quantitatively estimated using HAADF-STEM image analysis in correlation with AES and it is found between the range of ∼15–20 % in MSSE alloy. A 10-fold high photoresponsivity in the case of MSSE concerning as-grown MS having fast photocurrent growth time and the prolonged decay time originates from the ‘Se’ and this alloy assisted states to enhance the PEC performance of MSSE alloy. The enhanced PEC HER activity of MSSE alloy was identified in terms of overpotential and current density. In addition, increased density of states as a function of ‘Se’ alloying, shifts in a p-band centre and lowers ΔGH* according to density functional theory calculations, which makes MSSE alloy an efficient HER activity. Further, the PEC stability and presence of the ‘S–Se’ and ‘Se2’ alloying and their role towards HER have been correlated by the spectral line shape analysis of PL and Raman spectra from post-PEC HER catalysts. These experimental and theoretical findings establish the role of chalcogen, and transition metal-based 2D alloy, leading to the design of new PECs of engineered 2D atomic layer interfaces.

  • Core-shell nanofibers of ZnFe2O4/ZnO for enhanced visible-light photoelectrochemical performance

    Andrii Lys, Viktor Zabolotnii, Mária Čaplovičová, Iryna Tepliakova, Agris Berzins, Martin Sahul, Ľubomír Čaplovič, Alexander Pogrebnjak, Igor Iatsunskyi, Roman Viter

    In: Journal of Alloys and Compounds, Volume 984, 15 May 2024, 173885


    Recent research places significant importance on the development of innovative nanocomposites for photoelectrochemical applications. This paper presents the fabrication, characterization, and possible photoelectrochemical applications of novel ZnFe2O4/ZnO core-shell nanofibers. These core-shell nanofibers were fabricated through co-axial electrospinning using PVP solutions containing iron and zinc nitrate precursors for the core and shell. The structural and optical properties of ZnFe2O4/ZnO core-shell nanofibers were examined through TEM, SEM, XRD, FTIR, Raman spectroscopy, and diffuse reflectance spectroscopy. This comprehensive analysis unveiled that the development of core and shell characteristics was notably influenced by the interdiffusion of [Fe]/[Zn] during the annealing process. The photoelectrochemical properties of ZnFe2O4/ZnO core-shell nanofibers were assessed through electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and the Mott-Schottky method. These core-shell nanofibers demonstrated a robust electrochemical response to visible light. Photocurrent and photoconversion efficiency of the core-shell nanofibers were calculated and compared with the corresponding values for core-shell nanoparticles. The mechanisms underlying the structural, optical, and photoelectrochemical properties of ZnFe2O4/ZnO core-shell nanofibers were discussed. These advanced nanofibers hold potential applications in photocatalysis, photovoltaics, and energy storage, making this research timely and crucial for advancing sustainable energy technologies and environmental remediation efforts.

  • Effect of bias voltage on the structural properties of WN/NbN nanolayer coatings deposited by cathodic-arc evaporation

    K. Smyrnova, M. Sahul, M. Haršáni, Ľ. Čaplovič, V. Beresnev, Mária Čaplovičová, M. Kusy and A. Pogrebnjak

    In: J. Phys.: Conf. Ser. 2712 012014, 2024


    In this work, WN/NbN nanolaminate coatings were synthesized by cathodic-arc physical vapor deposition (CA-PVD) technique on a stainless-steel substrate. The paper reports the microstructure, cross-sectional morphology, surface roughness, and adhesion strength changes caused by variations in the absolute values of the negative substrate bias voltage, Us, in the 50-200 V range. Synthesized coatings were analyzed by Grazing incidence X-ray diffraction (GI-XRD), scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), laser scanning confocal microscopy (LSCM), and Daimler-Benz test. The phase analysis revealed that multilayer coatings had complex polycrystalline microstructure. They consisted of face-cantered cubic (fcc) β-W2N, fcc δ-NbN, and hexagonal ε-NbN phases. The total thickness and surface roughness had a descending trend with an increase in the absolute value of the negative bias voltage. Moreover, the WN/NbN coating deposited at Us = -50 V demonstrated the best adhesion strength to the substrate, suitable for protective coatings.

  • Oil Adsorption Behavior of N-doped, Co-decorated Graphene/Carbon Nanotube/Cellulose Microfiber Aerogels: A Comprehensive Investigation of Composite Component’s Effect


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

    In: Surfaces and Interfaces, (2024)


    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.

  • Type-II CdSe/ZnO Core/Shell Nanorods: Nanoheterostructures with A Tunable Dual Emission in Visible and Near-Infrared Spectral Ranges

    Anamul Haque, Filip Zechel, Viliam Vretenár, Mrinmoy Roy, Milan Sýkora

    In: Adv. Funct. Mater. 2023, 2305296


    A synthesis and characterization of luminescent nano-heterostructures consisting of CdSe nanorod (NR) cores and a ZnO shell with up to three monolayers of ZnO is reported. The core/shell heterostructures show a tunable, dual photoluminescence (PL) in visible and Near Infrared (NIR) spectral ranges. Upon shelling the visible PL band attributed to the carrier recombination within the CdSe core shifts to lower energy by ≈0.05 to 0.15 eV relative to the bare CdSe NRs, due to a reduced quantum confinement. A NIR band, observed ≈0.4 – 0.5 eV below the PL energy of the CdSe core, is attributed to a type-II carrier recombination across the CdSe/ZnO interface. The total PL quantum yield (PLQY) in the brightest heterostructures reaches ≈20%, increasing ≈100-fold over the PLQY of the corresponding bare CdSe NRs. The average lifetimes of the visible PL in some heterostructures exceeds 100 ns, compared to ≈5 ns lifetime typical for bare CdSe NRs. The average PL lifetimes attributed to the type-II charge separated states exceed one microsecond. Strong NIR PL, tunable in the 800–900 nm spectral range and the long-lived charge separated state make the CdSe/ZnO core-shell NRs appealing materials for exploitation in applications such as bioimaging, photocatalysis and optoelectronics.

  • Cobalt-doped WSe2@conducting polymer nanostructures as bifunctional electrocatalysts for overall water splitting

    Sadik Cogal, Gamze Celik Cogal, Matej Mičušík, Mário Kotlár, Maria Omastová

    In: International Journal of Hydrogen Energy, (2023)


    Designing of high-performance, low-cost, and nonprecious metal-based bifunctional electrocatalysts is highly significant for the development of water splitting process and expanding the practical application of green hydrogen production. Transition metal dichalcogenides (TMDs) with intrinsic physical and chemical properties have been considered potential catalytic materials for electrode fabrication. However, it has remained challenging to develop TMD catalysts that have bifunctional properties for overall water splitting. Herein, WSe2, as a typical representative of TMDs, was utilized to design electrocatalysts using polypyrrole (PPy) or polyaniline (PANI) as a conducting polymer (CP) and cobalt doping. A facile hydrothermal preparation of WSe2 in the presence of CP enabled the construction of cobalt-doped WSe2@CP electrocatalysts. Morphological analysis indicated that the CP played an important role as a conductive template to enhance the distribution of WSe2 nanosheets, leading to higher surface area. In addition, cobalt doping led to the formation of defect structures and boosted the electrocatalytic activities of the catalysts for oxygen evolution reaction (OER).

  • Influence of process and heat input on the microstructure and mechanical properties in wire arc additive manufacturing of hot work tool steels

    Florian Pixner, Ricardo Buzolin, Fernando Warchomicka, Mária Dománková, Mária Čaplovičová, Florian Riedlsperger, Sebastian Fritsche, Marta Orłowska, Josef Domitner, Michael Lasnik, Norbert Enzinger 

    In: Materials Science and Engineering: A, Volume 888, 17 November 2023, 145799


    The present study demonstrates the suitability of wire arc additive manufacturing (AM) for hot work tool steel processing. Different arc welding techniques and energy inputs were applied and systematically compared to determine the deposition characteristics, microstructure and mechanical properties. All AM deposits show a sound visual appearance and full density without macroscopic imperfections, i.e. cracking. By adhering to a pre-defined interpass strategy, the cold metal transfer process can be used to achieve higher weld beads with lower dilution and faster build-up rates than the metal active gas process. The microstructure of the AM parts is comparable for all process configurations and consists of an α/α′-matrix with a finely dispersed vermicular and polygonal δ-ferrite network; no notable amount of retained austenite could be measured, but it could be observed by transmission electron microscopy embedded within the laths. Intensive precipitation of multiple molybdenum-based precipitates is observed along the interface matrix to δ-ferrite. In contrast, iron-based precipitates are predominantly found inside and at the boundaries of the laths of the matrix. Similarities are also evident in the mechanical properties, resulting in an average hardness of 380–390 HV1 and absorbed impact energy of 10–12 J at room temperature. High yield strength values of 1000–1100 MPa and ultimate tensile strength of 1200–1400 MPa were obtained. No significant differences in the measured mechanical properties could be noted regarding the specimen orientation, indicating the isotropy of the properties.

  • Ag2O nanocrystals prepared by mechanochemical decomposition of Ag7O8NO3

    Martin Škrátek, Mária Čaplovičová, Ľubomír Čaplovič, Patrícia Petrisková, Erik Šimon, Erik Rakovský, Peter Billik

    In: Materials Letters. Vol. 348, (2023)


    Our work focuses on the preparation of nanocrystalline Ag2O (n-Ag2O) by mechanochemical decomposition (MCD) of a paramagnetic compound of an empirical formula Ag7O8NO3. Electrochemically prepared millimetre-long needles of Ag7O8NO3 were high-energy ball milled (HEM) for 1 min, 3 min and 5 min. A gradual decomposition of Ag7O8NO3 to n-Ag2O and AgNO3 was observed. Ag2O nanocrystals form in an aggregated and spherical morphology with crystallite sizes ranging from ∼10 – 30 nm. n-Ag2O displayed weak ferromagnetism with the saturation magnetisation of 5×10–3 emu/g. The MCD of Ag7O8NO3 can be estimated as follows: 2Ag7O8NO3 → 6Ag2O + 2AgNO3 + 5O2.

  • Green Colloidal Synthesis of MoS2 Nanoflakes

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

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


    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.

  • Application of MXene for remediation of low-level radioactive aqueous solutions contaminated with 133Ba and 137Cs

    Vipul Vilas Kusumkar, Shalu Atri, Süleyman İnan, Maros Gregor, Tomas Roch, Hryhorii Makarov, Maria Caplovicova, Michal Galambos, Eva Viglasova, Gustav Plesch and Olivier Monfort

    In: Chem. Commun., 2023,59, 12007-12010


    MXene is an innovative multilayered material that has been prepared by an acid-salt (HCl + NH4F) etching route and tested for the removal of 133Ba and 137Cs in radioactive conditions for the first time. MXene has exhibited high uptake capacity of about 154.9 and 121.5 mg g−1 for 133Ba and 137Cs, respectively, in 0.01 mol L−1 solution and using 5 g L−1 of adsorbent at natural pH.