1. Dynamic and electrified ammonia synthesis enabled by magnetic heating of barium-promoted ruthenium catalystAnja Sedminek, Darko Makovec, Matej Huš, Anže Prašnikar, Stanislav S. Jakuškin, Blaž Likozar, Janvit Teržan, Sašo Gyergyek, 2026, izvirni znanstveni članek Ključne besede: magnetic heating, ammonia synthesis, barium promoted catalyst, electrification
Objavljeno v DiRROS: 25.03.2026; Ogledov: 301; Prenosov: 169
 Celotno besedilo (5,82 MB)
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2. Mn-induced stabilization of a ▫$\beta$▫-alumina-type defect structure in barium hexaferrite nanoplateletsDarko Makovec, Matic Poberžnik, Janvit Teržan, Tomaž Mertelj, Damjan Vengust, Goran Dražić, Darja Lisjak, Sašo Gyergyek, 2026, izvirni znanstveni članek Povzetek: Hexaferrite nanoplatelets exhibit size-dependent structural variations influencing their magnetic properties. Here, we synthesized Mn-substituted barium ferrite nanoplatelets via hydrothermal methods, achieving up to ∼27% Fe substitution. Advanced STEM and Raman analyses revealed depletion of Fe(2b) trigonal lattice sites and associated oxygen vacancies, forming a β-alumina-type ferrite structure─representing the first pure Ba2+ β-ferrite analogue. First-principles modeling confirmed the thermodynamic stabilization of this defected structure at higher Mn/Fe ratios. Mn substitution reduced nanoplatelet size and suppressed magnetic properties, which were restored upon annealing at 800 °C, reverting to the M-type hexaferrite structure with expected magnetic behavior. These findings elucidate nanoscale structural adaptations induced by chemical substitution and offer insights into tailoring the magnetic properties of barium ferrite nanoplatelets through controlled synthesis and post-treatment.
Objavljeno v DiRROS: 23.03.2026; Ogledov: 231; Prenosov: 207
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3. Synthesis of a magnetically heatable ceria–supported ruthenium catalyst via deposition of nanocrystalline ceria on silica-coated magnetic iron–oxide nanoparticlesNina Kosi Križaj, Jakov-Stjepan Pavelić, Miha Grilc, Sašo Gyergyek, Darko Makovec, 2026, izvirni znanstveni članek Povzetek: We report the synthesis of a ceria-based catalyst support containing embedded magnetic iron–oxide nanoparticles (IONPs) that enable heating under a high-frequency alternating magnetic field. The ≈11 nm IONPs, synthesized by co-precipitation of Fe2+/Fe3+ ions at room temperature, were coarsened to ≈18 nm through subsequent hydrothermal treatment at 120 ◦C and then coated with a ≈2 nm silica layer. The catalyst support was prepared by depositing nanocrystalline ceria (CeO2) onto the IONPs via controlled precipitation of Ce3+ ions in the presence of hexamethylenetetramine (HMTA) in aqueous suspension. When deposited directly on the iron oxide, ceria formed small agglomerates of ≈10 nm octahedral nanocrystallites, whereas deposition on silicacoated IONPs produced a homogeneous 3–6 nm-thick shell composed of ≈3 nm globular crystallites. Special attention was given to elucidating the mechanism of shell formation. The magnetic catalyst was obtained by precipitating Ru nanoparticles (1–2 nm) onto the ceria support. Morpho-structural characterization was performed by XRD, TEM, and aberration-corrected STEM. Static and dynamic magnetization measurements at room temperature were used to assess the magnetic and heating performance. At low field amplitudes (<15 mT), catalysts prepared with IONPs of both sizes exhibited similar specific absorption rates, whereas at higher amplitudes the larger IONPs demonstrated superior heating efficiency. The catalytic performance was demonstrated in the magnetically heated hydrogenation of the bio-based compound 5-(hydroxymethyl)furfural to 2,5-bis (hydroxymethyl)furan, showing high activity, 100 % selectivity, and excellent stability upon recycling.
Ključne besede: nanotechnology, catalyst synthesis, ceria, magnetic nanoparticles, catalysis by magnetic heating, biomass valorisation, transmission electron microscopy
Objavljeno v DiRROS: 14.01.2026; Ogledov: 449; Prenosov: 287
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4. The efficient magneto-mechanical actuation of cancer cells using a very low concentration of non-interacting ferrimagnetic hexaferrite nanoplateletsTanja Goršak, Eva Jarc Jovičić, Larisa Tratnjek, Igor Križaj, Borja Sepulveda, Josep Nogues, Mateja Erdani-Kreft, Toni Petan, Slavko Kralj, Darko Makovec, 2024, izvirni znanstveni članek Objavljeno v DiRROS: 06.01.2026; Ogledov: 407; Prenosov: 233
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6. Enhanced electrochemical dissolution of iridium oxide in acidic electrolytes through presence of metal ions : shortened lifetime and hope for recoveryRaghunandan Sharma, Per Morgen, Darko Makovec, Sašo Gyergyek, Shuang Ma Andersen, 2024, izvirni znanstveni članek Povzetek: Nanoparticulate Ir-oxides are frequently used as highly active and robust anode electrocatalysts for acidic water electrolyzers. While their dissolution during the electrolyzer operation is unsought, it could be a green route for recovery of Ir from the spent electrodes. In this study, we explore such a possibility and show that the electrochemical dissolution of Ir-oxides during a potential cycling treatment can be enhanced by introducing transition metal ions (such as Cu2+) in the acidic electrolyte. Dissolution of Ir from a nanoparticulate Ir-oxide containing electrode through potential cycling between 0.0 and 1.65 V in 1 M HCl increases by a factor of ∼3 in the presence of low concentrations (e.g. 10 mM) of Cu2+. Impact of the presence of the metal ions on the Ir-oxide dissolution mechanism is characterized. Cyclic deposition and stripping of the Cu2+ ion on the Ir-oxide may be attributed to the enhanced Ir dissolution, as evidenced by cyclic voltammograms studied in detail for Cu2+. Apart from exploration of the possibility of the electrochemical dissolution-based recovery of Ir from the spent Ir-oxide electrocatalysts, the study highlights the generally negative impacts of the presence of certain metal ions in the feedstock water on the electrocatalyst durability in acidic water electrolysis. Outcomes of this study are highly relevant for the fast-growing acidic water electrolysis industry.
Ključne besede: electrocatalysts, oxygen evolution reaction, acidic environment
Objavljeno v DiRROS: 05.01.2026; Ogledov: 557; Prenosov: 284
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10. Surface phase diagrams of pristine and hydroxylated barium hexaferrite surfaces from first-principles atomistic thermodynamicsMatic Poberžnik, Gabriela Herrero-Saboya, Darko Makovec, Darja Lisjak, Layla Martin-Samos, 2023, izvirni znanstveni članek Povzetek: Barium hexaferrite (BHF) is a ferrimagnet, whose hexagonal unit cell presents five iron crystallographic sites along the -axis. At the nanoscale, BHF nanoparticles grow in the form of platelets, characterized by a low thickness along its principal magnetization axis ( -axis), displaying uniaxial magnetic anisotropy with the easy axis pointing perpendicular to the platelet. This unique property of BHF nanoplatelets has lead to a variety of novel applications, which often require surface functionalization. However, it has been observed that the nanoplatelets display two different surface morphologies depending on the stage/conditions of preparation. To ground these experimental observations, we employ the ab initio thermodynamics framework to perform a systematic investigation of the thermodynamic stability of BHF bulk terminations under a wide range of chemical conditions. We calculate the surface phase diagrams of pristine and hydroxylated bulk terminations along the -axis. For pristine terminations, two different iron terminated surfaces are preferred: the barium containing 2b termination (Ba-rich conditions) and the 4f iron terminated surface (Ba-poor conditions). In the presence of water, the hydroxylated oxygen-terminated surfaces (12k-O) are identified as the most stable ones at Ba-poor conditions and low pH values, whereas the hydroxylated 2b surface is preferred at high pH and Ba-rich conditions.
Objavljeno v DiRROS: 15.04.2025; Ogledov: 975; Prenosov: 505
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