Author: Mária Čaplovičová

Dehydroaromatization of methane over Mo/ZSM-5 zeolites: influence of aluminum distribution in the crystals

Posted on by Mária Čaplovičová

HORŇÁČEK, Michal – HUDEC, Pavol – JORÍK, Vladimír – ČAPLOVIČOVÁ, Mária – ČAPLOVIČ, Ľubomír – KALIŇÁK, Michal – SMIEŠKOVÁ, Agáta

https://doi.org/10.1007/s11144-020-01887-5

Abstract

Mo/ZSM-5 type catalysts based on two ZSM-5 zeolites with comparable crystal morphology, shape and size, Si/Al in bulk (22–23), acidity and amount of Mo (~ 4.7 wt.%) but having a different (homogeneous and non-homogeneous) Al distribution in particles and different acid sites type distribution were investigated in methane dehydroaromatization. From the results follows that Mo is associated with both BAS and LAS in the samples with almost homogenous Al distribution (MoZSM-5/AH). In the case of both samples with non-homogenous Al distribution (MoZSM-5/BH and MoZSM-5/BNH4) Mo preferably associates with BAS. Evidently lower activity and selectivity of Mo/ZSM-5/AH catalyst in methane transformation compared with Mo/ZSM-5/BH we attribute to the fact that from Mo species which interact with Lewis acid sites in sample ZSM-5/AH less active carburized species are formed as from the Mo associated with Brønsted sites in sample ZSM-5/BH.

Green synthesis of stable nanocolloids of monodisperse silver and gold nanoparticles using natural polyphenols from fruits of Sambucus nigra L

Posted on by Mária Čaplovičová

MARIYCHUK, Ruslan – PORUBSKÁ, Jana – OSTAFIN, Marek – ČAPLOVIČOVÁ, Mária – ELIÁŠOVÁ, Adriana

In Applied Nanoscience. Vol. 10, iss. 12 (2020)

https://doi.org/10.1007/s13204-020-01324-y

Abstract

In the present work, we report, for the first time, the production of stable nanocolloids of highly monodisperse silver and gold nanoparticles (AgNPs and AuNPs) using phytosynthesis approach. With the aim to eliminate misinterpretations associated with the use of usually applied crude plant extracts, the presented study was focused on the use of polyphenolic fraction isolated from elderberry fruits (Sambucus nigra L.) for the synthesis. Obtained AgNPs and AuNP were characterized by UV–Vis and FTIR spectroscopy, DLS and TEM. We observed unexpectedly high capability of the natural polyphenols not only to form monodisperse nanoparticles but also to stabilise the concentrated nanocolloids (539 mg/L AgNPs and 739 mg/L AuNPs) for at least two years. Moreover, AgNPs showed strong antibacterial properties against pathogenic bacterial strains Staphylococcus aureus and Escherichia coli (inhibited after 15 min and totally stopped growth after 3 and 5 h at 3.125 mg/L concentration).

Ni-mediated reactions in nanocrystalline diamond on Si substrates: the role of the oxide barrier

Posted on by Mária Čaplovičová

TULIČ, Semir – WAITZ, Thomas – ROMANYUK, Oleksandr – VARGA, Marián – ČAPLOVIČOVÁ, Mária – HABLER, Gerlinde – VRETENÁR, Viliam – KOTLÁR, Mário – KROMKA, Alexander – REZEK, Bohuslav – SKÁKALOVÁ, Viera

In RSC Advances. Vol. 10, iss. 14 (2020)

https://doi.org/10.1039/D0RA00809E

Abstract

Nanocrystalline diamond (NCD) films grown on Si substrates by microwave plasma enhanced chemical vapor deposition (MWPECVD) were subjected to Ni-mediated graphitization to cover them with a conductive layer. Results of transmission electron microscopy including electron energy-loss spectroscopy of cross-sectional samples demonstrate that the oxide layer on Si substrates (∼5 nm native SiO2) has been damaged by microwave plasma during the early stage of NCD growth. During the heat treatment for graphitizing the NCD layer, the permeability or absence of the oxide barrier allow Ni nanoparticles to diffuse into the Si substrate and cause additional solid-state reactions producing pyramidal crystals of NiSi2 and SiC nanocrystals. The latter are found impinged into the NiSi2 pyramids but only when the interfacial oxide layer is absent, replaced by amorphous SiC. The complex phase morphology of the samples is also reflected in the temperature dependence of electrical conductivity, where multiple pathways of the electronic transport dominate in different temperature regions. We present models explaining the observed cascade of solid-state reactions and resulting electronic transport properties of such heterostructures.

Ti3+ doped anodic single-wall TiO2 nanotubes as highly efficient photocatalyst

Posted on by Mária Čaplovičová

MOTOLA, Martin – ČAPLOVIČOVÁ, Mária – KRBAL, Miloš – SOPHA, Hannah – THIRUNAVUKKARASU,  Guru Karthikeyan – GREGOR, Maroš – PLESCH, Gustáv – MACAK, Jan M.

In Electrochimica Acta. Vol. 331, (2020)

https://doi.org/10.1016/j.electacta.2019.135374

Abstract

In this work, a two-step treatment of TiO2 nanotube (TNT) layers towards enhanced photocatalytic performance is presented. TNT layers with a thickness of ∼7 μm and an average inner diameter of ∼190 nm were prepared via electrochemical anodization of Ti foil in a fluoride containing ethylene glycol-based electrolyte. To improve the photocatalytic activity of the produced TNT layers a two-step post-treatment was conducted. First, the inner shell of the native double-wall TNT layers was removed via a mild pre-annealing followed by a selective etching treatment of the inner shell in piranha solution yielding single-wall TNT layers. Second, reduction via annealing in H2/Ar atmosphere was performed. The resulting Ti3+ doped single-wall TNT layers possess 100% enhancement of photocatalytic activity compared to their non-treated counterparts.

Changes in microstructure of ledeburitic tool steel due to vacuum austenitizing and quenching, sub-zero treatments at – 140° and tempering

Posted on by Mária Čaplovičová

ĎURICA, Juraj – PTAČINOVÁ, Jana – DOMÁNKOVÁ, Mária – ČAPLOVIČ, Ľubomír – ČAPLOVIČOVÁ, Mária – HRUŠOVSKÁ, Linda – MALOVCOVÁ, Veronika – JURČI, Peter

In Vacuum. Vol. 170, (2019)

https://doi.org/10.1016/j.vacuum.2019.108977

Abstract

The microstructure of Vanadis 6 ledeburitic steel subjected to sub-zero treatments at −140 °C for different durations followed by various tempering regimes was investigated. The obtained results infer that: i) retained austenite amount is fivefold reduced by this treatment, and compressive stresses higher than 1500 MPa are generated in this phase, ii) martensite is refined due to SZT, and it contains enhanced number of crystal defects, iii) great number of “extra” cementitic carbides is formed during the sub-zero period; this number is higher than what is achieved by sub-zero treatments at −196 °C, iv) the number of “extra” carbides decreases with tempering, however, it remains higher than after in both the conventionally quenched and sub-zero treated at −196 °C steel, v) sub-zero treatments at −140 °C modify the precipitation behaviour substantially; coherent nano-sized ε-carbides and cementite were found already prior tempering the steel, and besides the cementite also M7C3 phase was detected after tempering treatment.

Tuning the orientation of few-layer MoS2 films using one-zone sulfurization

Posted on by Mária Čaplovičová

SOJKOVÁ, Michaela – VÉGSÖ, Karol – MRKYVKOVA, Naďa – HAGARA, Jakub – HUTÁR, Peter – ROSOVÁ, Alica – ČAPLOVIČOVÁ, Mária – LUDACKÁ, Uršula – SKÁKALOVÁ, Viera – MAJKOVÁ, Eva – ŠIFFALOVIČ, Peter – HULMAN, Martin

In RSC Advances. Vol. 9, iss. 51 (2019)

https://doi.org/10.1039/C9RA06770A

Abstract

Few-layer MoS2 films are promising candidates for applications in numerous areas, such as photovoltaics, photocatalysis, nanotribology, lithium batteries, hydro-desulfurization catalysis and dry lubricants, especially due to their distinctive electronic, optical, and catalytic properties. In general, two alignments of MoS2 layers are possible – the horizontal and the vertical one, having different physicochemical properties. Layers of both orientations are conventionally fabricated by a sulfurization of pre-deposited Mo films. So far, the Mo thickness was considered as a critical parameter influencing the final orientation of MoS2 layers with horizontally and vertically aligned MoS2 grown from thin (1 nm) and thick (3 nm) Mo films, respectively. Here, we present a fabrication protocol enabling the growth of horizontally or vertically aligned few-layer MoS2 films utilizing the same Mo thickness of 3 nm. We show that the sulfur vapor is another parameter influencing the growth mechanism, where a sulfurization with higher sulfur vapor pressure leads to vertical MoS2 layers and slow sulfur evaporation results in horizontally aligned layers for a thicker Mo starting layer.

Stoichiometry, structure and mechanical properties of co-sputtered Ti 1-x Ta x B 2±Δ coatings

Posted on by Mária Čaplovičová

GRANČIČ, B. – PLEVA, Milan – MIKULA, M. – ČAPLOVIČOVÁ, Mária – SATRAPINSKYY, L – ROCH, Tomáš – TRUCHLÝ, M. – SAHUL, Martin – GREGOR, M. – ŠVEC, Peter, Sr. – ZAHORAN, Miroslav – KÚŠ, Peter

In Surface & Coatings Technology. Vol. 367, June (2019)

https://doi.org/10.1016/j.surfcoat.2019.04.017

Abstract

Magnetron co-sputtering from TiB2 and TaB2 stoichiometric targets is used to prepare AlB2-prototype ternary Ti1-xTaxB2±Δ solid solution, with x in the range from 0 to 1. Using this technique, the boron-to-metal ratio (B/Me) varies with the actual Ti and Ta content. The boron-to‑tantalum ratio can be increased by decreasing the TaB2 target voltage, which has a considerable effect on the coating structure. Coatings with B/Me > 2 reveal highly textured nanocolumnar structure, while the coatings with B/Me < 2 tend to be nanocrystalline (without any preferred crystallite orientation) or amorphous. All the deposited coatings have a hardness higher than 32 GPa. The under-stoichiometric (B/Me < 2) coatings show material pile-up around the cube-corner indent edges, an indication for plastic flow and increased ductility.

Structure of superconducting MgB2 thin films prepared by vacuum evaporation and ex-situ annealing in Ar and O-2 atmospheres

Posted on by Mária Čaplovičová

ROCH, Tomáš – GREGOR, Maroš – ŠVEC, Peter, Jr. – PLECENÍK, Tomáš – SATRAPINSKYY, Leonid – ČAPLOVIČOVÁ, Mária – BYSTRICKÝ, Roman – KÚŠ, Peter – PLECENÍK, Andrej

In Applied Surface Science. Vol. 461, (2018)

https://doi.org/10.1016/j.apsusc.2018.05.038

Abstract

Superconducting MgB2 thin films were fabricated on c-cut sapphire substrates by vacuum co-evaporation of magnesium and boron followed by an ex situ post-annealing. We show that annealing in oxygen atmosphere can significantly improve the superconducting properties of the MgB2 thin films compared to the typical annealing in argon atmosphere. In this work, influence of the ex-situ annealing atmosphere on the structure, texture and morphology of the superconducting MgB2 thin films has been studied by transmission electron microscopy, X-ray diffraction and pole figure measurements. Samples annealed at 800 °C in Ar, at 800 °C in O2 and at 500 °C in O2 have been compared. The annealing in O2 at 800 °C produces MgB2 thin films with the highest superconducting transition temperature and critical current density. We show that this is thanks to the thickest MgO layer at the surface produced in this case, which acts as a protecting barrier against out-diffusion of Mg during the annealing and leads to better stoichiometry and larger MgB2 grains compared to the samples annealed in Ar. Our method can be alternative to the customary ex-situ post annealing of Mg-B precursor in sealed vapor cell. In all samples, the MgB2 phase showed single axis texture with the (0 0 0 1) planes slightly inclined by 0° to 15° with respect to the Al2O3(0 0 0 1) substrate surface incurred with the initial precursor evaporation geometry. During the annealing, the excess Mg also reacts with the Al2O3 substrate and minor MgAl2O4 and MgO phases are produced at the substrate-layer interface.