• 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.

  • Tailoring the electronic properties of the SnO2 nanoparticle layer for n-i-p perovskite solar cells by Ti3C2TX MXene

    Muhammad Faraz Ud Din, Shima Sousani, Mário Kotlár, Sami Ullah, Maros Gregor, Tomas Scepka, Yaryna Soyka, Anastasiia Stepura, Ashin Shaji, Femi Igbari, Karol Vegso, Vojtech Nadazdy, Peter Siffalovic, Matej Jergel, Maria Omastova, Eva Majkova

    In: Materials Today Communications, Volume 36, (2023)


    The effect of the Ti3C2Tx MXene modification of the SnO2 electron transport layer (ETL) was studied for the concentration range 0–7.4 wt% MXene. The electronic properties of the MXene-modified ETL were studied by the electrical conductivity measurements, density of states mapping by the energy-resolved electrochemical impedance spectroscopy, ultraviolet photoelectron spectroscopy, and photoluminescence. The structure and morphology of the MXene-modified ETL and the top perovskite layer were analyzed by the scanning electron microscopy (SEM), scanning transmission electron microscopy, grazing-incidence X-ray diffraction and in situ grazing-incidence wide-angle X-ray scattering (GIWAXS). The increased electrical conductivity and electron selectivity for the MXene-modified SnO2 ETL was confirmed up to 1 wt% MXene. For 7.4 wt% MXene, significant suppression of the hole blocking property of the ETL was found. The in situ GIWAXS was performed during the post-deposition annealing of the perovskite layer. The increased perovskite grain size on the SnO2 ETL modified by MXene compared to the pure SnO2 ETL visible by SEM was confirmed. The uniaxial texture of the perovskite crystals was revealed in both cases with an increased misorientation angle for the MXene-modified ETL. The grain size and misorientation angle do not exhibit any systematic temporal changes during the post-deposition annealing. The increasing number of the grains during the annealing was observed. These results are explained using the nucleation and growth model. The increased power conversion efficiency from 17.4% to 18.3% of the archetypal methylammonium-lead-iodide perovskite solar cell after the modification of the SnO2 ETL with 0.1 wt% MXene is the effect of two contributions – increased electrical conductivity of the ETL and improved crystallinity and larger grain size compared to the pure SnO2 ETL, which lowers the total boundary area and charge recombination at trap states typically formed at grain boundaries.

  • Thermoplastic starch/bentonite clay nanocomposite reinforced with vitamin B2: Physicochemical characteristics and release behavior

    Abolfazl Heydari, Milad KhajeHassani, Haniyeh Daneshafruz, Sepideh Hamedi, Faeze Dorchei, Mário Kotlár, Fahimeh Kazeminava, Samahe Sadjadi, Farideh Doostan, Ivan Chodak, Hassan Sheibani

    In: International Journal of Biological Macromolecules. Vol. 242, (2023)


    This study presents the development and characterization of a nanocomposite material, consisting of thermoplastic starch (TPS) reinforced with bentonite clay (BC) and encapsulated with vitamin B2 (VB). The research is motivated by the potential of TPS as a renewable and biodegradable substitute for petroleum-based materials in the biopolymer industry. The effects of VB on the physicochemical properties of TPS/BC films, including mechanical and thermal properties, water uptake, and weight loss in water, were investigated. In addition, the surface morphology and chemical composition of the TPS samples were analyzed using high-resolution SEM microscopy and EDS, providing insight into the structure-property relationship of the nanocomposites. The results showed that the addition of VB significantly increased the tensile strength and Young’s modulus of TPS/BC films, with the highest values observed for nanocomposites containing 5 php of VB and 3 php of BC. Furthermore, the release of VB was controlled by the BC content, with higher BC content leading to lower VB release. These findings demonstrate the potential of TPS/BC/VB nanocomposites as environmentally friendly materials with improved mechanical properties and controlled release of VB, which can have significant applications in the biopolymer industry.

  • GaAs ablation with ultrashort laser pulses in ambient air and water environments

    Edgaras Markauskas,  Laimis Zubauskas, Arnas Naujokaitis, Bronislovas Čechavičius, Martynas Talaikis, Gediminas Niaura, Mária Čaplovičová, Viliam Vretenár, Tadas Paulauskas

    In: Journal of Applied Physics. Vol. 133, iss. 23 (2023)


    Water-assisted ultrashort laser pulse processing of semiconductor materials is a promising technique to diminish heat accumulation and improve process quality. In this study, we investigate femtosecond laser ablation of deep trenches in GaAs, an important optoelectronic material, using water and ambient air environments at different laser processing regimes. We perform a comprehensive analysis of ablated trenches, including surface morphological analysis, atomic-resolution transmission electron microscopy imaging, elemental mapping, photoluminescence, and Raman spectroscopy. The findings demonstrate that GaAs ablation efficiency is enhanced in a water environment while heat-accumulation-related damage is reduced. Raman spectroscopy reveals a decrease in the broad feature associated with amorphous GaAs surface layers during water-assisted laser processing, suggesting that a higher material quality in deep trenches can be achieved using a water environment.