UČAKAR, Aleksander, KOCJAN, Andraž, BELEC, Blaž, KOŠIR, Janez, KALLIO, Tanja, MAČEK, Marjeta, ARAH, Bor, JENUŠ, Petra. The role of carbon presence on the strontium hexaferrite phase decomposition during pressureless spark plasma sintering (pSPS). Open ceramics. [in press] 2025, vol. , [article no.] 100804, str. 1-21

Sr-hexaferrite ceramics were rapidly sintered via pressureless spark plasma sintering (pSPS) in a graphite crucible under vacuum. Modeling of the temperature profile revealed that the reductive environment caused phase decomposition into Sr-rich and Sr-deficient phases, degrading magnetic properties. Some new phases had lower melting points, shifting the sintering mechanism from solid-state to partial liquid-phase sintering.

BASHRI, Mahira, KUMAR, Sushil, BHANDARI, Pallab, STEPHEN, Sasi, O'CONNOR, Matthew J., GABER, Safa, ŠKORJANC, Tina, FINŠGAR, Matjaž, LUCKACHAN, Gisha Elizabeth, BELEC, Blaž, et al. Hydrazone-linked covalent organic framework catalyst via efficient Pd recovery from wastewater. ACS applied materials & interfaces. 

A hydrazone-linked COF (Tfpa-Od) was used for efficient Pd²⁺ recovery from wastewater, showing high selectivity (up to 100%) and a strong adsorption capacity (372.6 mg/g; Kd = 3.62 × 10⁶ mL/g). Its electron-rich framework enables Pd capture and subsequent reuse as a catalyst in Suzuki–Miyaura reactions, demonstrating good activity and recyclability. This approach supports sustainable Pd recovery and promotes circular economy practices.

BELEC, Blaž, KOSTEVŠEK, Nina, DELLA PELLE, Giulia, NEMEC, Sebastjan, KRALJ, Slavko, BERGANT MARUŠIČ, Martina, GARDONIO, Sandra, FANETTI, Mattia, VALANT, Matjaž. Silica coated Bi2Se3 topological insulator nanoparticles : an alternative route to retain their optical properties and make them biocompatible. Nanomaterials. 

Bi₂Se₃ nanoparticles exhibit strong photothermal effects due to localized surface plasmon resonance from topological surface states. To improve stability and biocompatibility, we coated the nanoparticles with silica instead of ethylene glycol, which was shown to mask optical properties and be cytotoxic. Silica-coated Bi₂Se₃ retained photothermal performance (except at ~200 nm thickness) and showed significantly improved heat conversion, requiring much lower concentrations. In vitro tests confirmed their biocompatibility, making them promising for medical applications.

MAVRIČ, Andraž, ŽERJAV, Gregor, BELEC, Blaž, ROŠKARIČ, Matevž, FINŠGAR, Matjaž, PINTAR, Albin, VALANT, Matjaž. Structural disorder of AlMg-oxide phase supporting Cu/ZnO catalyst improves efficiency and selectivity for CO2 hydrogenation to methanol. ChemCatChem. Jul. 2023, vol. 15, issue 13, str. 1-8, ilustr. ISSN 1867-3880.

The performance of the Cu/ZnO catalyst system with the AlMg-oxide phase is studied for CO₂ hydrogenation to methanol. The catalyst is prepared by thermal treatment of the hydrotalcite phase containing intimately mixed metal cations in the hydroxide form. CuO in the presence of ZnO and disordered AlMg-oxide phase gets easily reduced to Cu during the hydrogenation reaction. Its catalytic activity at relatively low Cu metal content (∼14 at.%) remains stable during 100 hours on stream at 260 °C with constant space-time yield for methanol (∼1.8 g_MeOH g_cat⁻¹ h⁻¹) and high methanol selectivity (>85 %) The improved performance is attributed to the neutralization of surface acidity, increased number of weak basic sites in the disordered phase, and lower tendency for coke formation.

RMUŠ, Jelena, BELEC, Blaž, MILANOVIĆ, Igor, FANETTI, Mattia, GARDONIO, Sandra, VALANT, Matjaž, KURKO, Sandra V. Composites of transition metal dichalcogenides and topological insulators as catalytic materials for HER. Journal of energy storage. Sep. 2023, vol. 68, [article no.] 107719, str. 1-11, 

We developed composite catalysts combining MoS₂, a transition metal dichalcogenide, with Bi₂Se₃, a topological insulator, to improve hydrogen evolution reaction (HER) activity. Composites were prepared by mechanical milling, high-power sonication, and spin-coating using hydrothermally synthesized precursors. Structural and morphological features were linked to electrochemical performance through impedance spectroscopy and voltammetry. Mechanical milling induced the greatest defect density, significantly enhancing catalytic activity and lowering the overpotential for 10 mA/cm² current density by up to 50 mV. Bi₂Se₃ facilitates electron transfer to MoS₂, reducing charge transfer resistance by 25 Ω, highlighting the synergistic effect in boosting HER efficiency.

MEHTA, Akansha, RATHER, Rayees Ahmad, BELEC, Blaž, GARDONIO, Sandra, FANG, Ming, VALANT, Matjaž. Plastic waste precursor-derived fluorescent carbon and construction of ternary FCs@CuO@TiO2 hybrid photocatalyst for hydrogen production and sensing application. Energies. 2022, vol. 15, iss. 5, str. 1-16, ilustr. ISSN 1996-1073.

This study presents a cost-effective and eco-friendly approach linking plastic waste management, wastewater treatment, and renewable hydrogen generation. Fluorescent carbon nanoparticles (FCs) were hydrothermally synthesized from low-density polyethylene (LDPE) waste and demonstrated sensitive detection of Cu²⁺ ions in water with a low detection limit of 86.5 nM. The Cu²⁺-loaded FCs were combined with TiO₂ to form a ternary FCs@CuO@TiO₂ composite, which exhibited enhanced photocatalytic hydrogen production under simulated solar light, achieving an H₂ evolution rate of ~1800 μmol g⁻¹ and a solar-to-hydrogen efficiency of ~0.95%. This performance results from the fluorescent properties of FCs and the synergistic CuO-TiO₂ interaction, improving light absorption and charge separation, offering a promising sustainable route for waste valorization and clean energy.

D'ELIA, Alessandro, REZVANI, S. J., ZEMA, Nicola, ZUCCARO, F., FANETTI, Mattia, BELEC, Blaž, LI, B. W., ZOU, C. W., SPEZZANI, Carlo, SACCHI, Maurizio, MARCELLI, Augusto, CORENO, Marcello. Stoichiometry and disorder influence over electronic structure in nanostructured VOx films. Journal of nanoparticle research. 2021, vol. 23, iss. 1, str. 1-9, ilustr. ISSN 1388-0764.

We investigate how nanoparticle size and stoichiometry influence the local atomic structure of VOx nanostructured films using in situ X-ray absorption near-edge structure (XANES) spectroscopy. Focusing on VO₂, we reveal that nanoscale size disrupts the bulk ligand symmetry, creating a continuum of distorted atomic configurations. This leads to stoichiometry-dependent disorder in the ligand matrix and modulation of the electronic structure. Our findings open pathways to novel disordered VOx phases and offer a powerful approach to study complex oxide nanomaterials.

DE JULIÁN FERNÁNDEZ, Cesár, SANGREGORIO, Claudio, DE LA FIGUERA, Juan, BELEC, Blaž, MAKOVEC, Darko, QUESADA, Adrian. Progress and prospects of hard hexaferrites for permanent magnet applications : topical review. Journal of physics. D, Applied physics. 2021, vol. 54, no. 15, str. 1-30. ISSN 0022-3727.

Permanent magnets based on hard hexaferrite represent the largest family of magnets being used today by volume. They generate moderate remanence induction, but present crucial advantages in terms of availability, cost, resistance to demagnetization and corrosion and absence of eddy current losses. As a consequence, ferrites are the most logical candidate for substitution of rare-earths in selected applications that do not demand the best performing magnets. If the remanence of ferrite-based magnets was to be improved, even mildly, the door to a larger scale substitution could be opened. In this framework, we review here current strategies to improve the properties of hexaferrites for permanent magnet applications. We first discuss the potential of exploring the nanoscale. Second, progress related to controllably doping hexaferrites is revised. Third, results achieved by fabricating hard-soft magnetic composites using ferrites as the hard phase are presented. Finally, future prospects and new potential end applications for ferrite magnets are discussed

D'ELIA, Alessandro, CEPEK, Cinzia, SIMONE, Monica de, MACIS, Salvatore, BELEC, Blaž, FANETTI, Mattia, PISERI, Paolo, MARCELLI, Augusto, CORENO, Marcello. Interplay among Work Function, electronic structure and stoichiometry in nanostructured VOxVOx films. PCCP. Physical chemistry chemical physics : a journal of European Chemical Societies. 2020, vol. 22, iss. 11, str. 6282-6290, ilustr. ISSN 1463-9076

We synthesized vanadium oxide nanostructured films with controlled stoichiometry and work function (3.7–7 eV) using room-temperature supersonic cluster beam deposition. Through in situ Auger and valence-band photoemission spectroscopy, we revealed how oxygen content and hybridization of V 3d, O 2p, and V 4s states shape the electronic structure. Our findings show that precise stoichiometry control enables tuning of the work function, with nanoscale quantum confinement further enhancing it beyond bulk values—key for optimizing oxide materials in electronic and energy applications.

BELEC, Blaž, FERFOLJA, Katja, GORŠAK, Tanja, KOSTEVŠEK, Nina, GARDONIO, Sandra, FANETTI, Mattia, VALANT, Matjaž. Inherent surface properties of adsorbent-free ultrathin Bi2Se3 topological insulator platelets. Scientific reports. 2019, vol. 9, str. 190571-1-19057-9, ilustr. ISSN 2045-2322. https://doi.org/10.1038/s41598-019-55646-1

We demonstrate a novel hydrothermal method for synthesizing ultra-thin hexagonal Bi₂Se₃ platelets without using organic reactants, resulting in particles with truly clean surfaces. This allowed, for the first time, direct measurement of their intrinsic surface charge and optical properties, including localized surface plasmon resonance linked to topological surface states. The clean synthesis approach overcomes limitations of conventional solvothermal methods and opens new possibilities for studying and applying Bi₂Se₃ in plasmonic and topological materials research.

MAKOVEC, Darko, GYERGYEK, Sašo, GORŠAK, Tanja, BELEC, Blaž, LISJAK, Darja. Evolution of the microstructure during the early stages of sintering barium hexaferrite nanoplatelets. Journal of the European ceramic society. [Print ed.]. 2019, vol. 39, iss. 15, str. 4831-4841, ilustr. ISSN 0955-2219.

This study explores how the distinct iron-rich structure of hydrothermally synthesized barium hexaferrite nanoplatelets influences microstructural development during sintering. Through advanced microscopy and magnetic analysis, we show that fusion of nanoplatelets drives grain thickening, often leading to planar defects and Fe₂O₃ formation. Notably, Sc-substitution induces superstructural ordering and exaggerated grain growth, providing valuable insight for tailoring hexaferrite ceramics.

GORŠAK, Tanja, MAKOVEC, Darko, JAVORNIK, Uroš, BELEC, Blaž, KRALJ, Slavko, LISJAK, Darja. A functionalization strategy for the dispersion of permanently magnetic barium-hexaferrite nanoplatelets in complex biological media. Colloids and surfaces. A, Physicochemical and Engineering Aspects. [Print ed.]. 2019, vol. 573, str. 119-127. ISSN 0927-7757. DOI: 10.1016/j.colsurfa.2019.04.051. 

We present a breakthrough strategy for stabilizing nanoparticles in complex biological environments—a key challenge in nanomedicine. Using a covalent dextran coating anchored via a silane linker, we ensured long-term colloidal stability even for highly agglomeration-prone barium hexaferrite nanoplatelets. This multi-step method overcomes limitations of conventional coatings and enables the use of magnetic nanoplatelets in biomedical applications, with stability verified by TEM, NMR, and dynamic light scattering.

MAKOVEC, Darko, KOMELJ, Matej, DRAŽIĆ, Goran, BELEC, Blaž, GORŠAK, Tanja, GYERGYEK, Sašo, LISJAK, Darja. Incorporation of Sc into the structure of barium-hexaferrite nanoplatelets and its extraordinary finite-size effect on the magnetic properties. Acta materialia. [Print ed.]. Jun. 2019, vol. 172, str. 84-91, ilustr. ISSN 1359-6454.

This study reveals a striking reversal in magnetic behavior between bulk and nanoscale barium hexaferrite. While Sc-substitution reduces magnetization in bulk, it significantly enhances it in nanoplatelets. Using atomic-resolution microscopy and simulations, we show that this unexpected boost in saturation magnetization arises from unique two-dimensional magnetic ordering at the nanoscale—offering new insights for engineering high-performance magnetic nanomaterials.

MAKOVEC, Darko, BELEC, Blaž, GORŠAK, Tanja, LISJAK, Darja, KOMELJ, Matej, DRAŽIĆ, Goran, GYERGYEK, Sašo. Discrete evolution of the crystal structure during the growth of Ba-hexaferrite nanoplatelets. Nanoscale. 2018, vol. 10, iss. 30, str. 14480-14491, ilustr. ISSN 2040-3364.

We investigated how the crystal structure of barium hexaferrite nanoplatelets evolves during low-temperature hydrothermal synthesis. Starting with ultra-thin SRS*-structured platelets, we observed discrete growth via RS segment additions, directly impacting their magnetic properties. This stepwise structural adaptation links nanoscale morphology with magnetism, offering insights for designing functional magnetic nanomaterials for advanced technologies.

BELEC, Blaž, DRAŽIĆ, Goran, GYERGYEK, Sašo, PODMILJŠAK, Benjamin, GORŠAK, Tanja, KOMELJ, Matej, NOGUÉS, Julio J., MAKOVEC, Darko. Novel Ba-hexaferrite structural variations stabilized on the nanoscale as building blocks for epitaxial bi-magnetic hard/soft sandwiched maghemite/hexaferrite/maghemite nanoplatelets with out-of-plane easy axis and enhanced magnetization. Nanoscale. 2017, vol. 9, no. 44, str. 17551-17560. ISSN 2040-3372. DOI: 10.1039/C7NR05894B. 

Atomic-resolution microscopy revealed a unique nanoscale structure of barium hexaferrite (BHF) nanoplatelets, enabling strong uniaxial magnetic anisotropy. By epitaxially coating them with maghemite layers, we formed uniform M/BHF/M composite nanoplatelets with significantly enhanced magnetization. These engineered nanostructures hold promise for advanced magnetic applications requiring directional alignment and improved performance.

PLOHL, Olivija, KRAFT, Marco, KOVAČ, Janez, BELEC, Blaž, PONIKVAR-SVET, Maja, WÜRTH, Christian, LISJAK, Darja, RESCH-GENGER, Ute. Optically detected degradation of NaYF4:Yb,TmNaYF4:Yb,Tm-based upconversion nanoparticles in phosphate buffered saline solution. Langmuir. 2017, vol. 33, no. 2, str. 553-560. ISSN 0743-7463. DOI: 10.1021/acs.langmuir.6b03907.

This proof-of-concept study evaluates analytical methods to monitor the stability of β-NaYF₄:Yb³⁺,Tm³⁺ upconversion nanoparticles in phosphate-buffered saline. By combining fluoride ion release measurements, XPS surface analysis, and fluorescence techniques, we identified the 800 nm luminescence lifetime as the most effective indicator of nanoparticle stability and surface chemistry changes under physiological conditions.