1. Razvoj magnetno segrevanih katalizatorjev za kemijsko hrambo vodika : doktorska disertacijaAnja Sedminek, 2025, doctoral dissertation Abstract: Doktorska disertacija obravnava razvoj inovativnih magnetno odzivnih nanokompozitov, namenjenih uporabi kot nosilcev katalizatorjev za elektrificirane kemijske procese. Uporaba izmeničnega magnetnega polja omogoča lokalizirano, hitro in selektivno segrevanje katalitskega sloja, kar predstavlja alternativo klasičnim načinom gretja ter prispeva k večji energetski učinkovitosti in združljivosti procesov z obnovljivimi viri energije.
Glavni cilj doktorske disertacije je bil razvoj in karakterizacija novih magnetnih materialov za tehnologijo magnetno segrevane katalize ter preizkus njihove aktivnosti v procesih, ki omogočajo pretvorbo električne energije v kemijsko, kot je shranjevanje energije v molekulah, bogatih z vodikom. Preučili smo dva ključna primera: shranjevanje energije v obliki amonijaka (NH₃) ter v tekočih organskih nosilcih vodika (LOHC).
Za ta namen smo razvili postopek priprave CoxNi1-x-Al₂O₃ nanokompozitov, prenosljiv na večjo skalo, v katerih so zlitinski nanodelci CoNi (~ 15 nm) homogeno porazdeljeni po porozni matrici iz aluminijevega oksida. Ti materiali imajo visoko specifično površino (~150 m² g⁻¹), so stabilni in se učinkovito segrevajo (≥ 500 °C, 25 mT), ko so izpostavljeni izmeničnemu magnetnemu polju. Nanos rutenijevih nanodelcev (1 ut.%, 2-7 nm) in njihova promocija z barijem (4,5 ut.%) sta omogočila pripravo katalizatorjev z visoko disperzijo (54 %) ter dobro pokritostjo (52 %) aktivnih mest.
Eksperimenti sinteze in razgradnje amonijaka so potekali v namensko izdelanem kvarčnem reaktorju, ki omogoča obratovanje pri povišanih tlakih. Rezultati kažejo, da z barijem promoviran rutenijev katalizator pri sintezi NH₃ doseže reakcijsko hitrost 1600 mmol NH₃ gRu⁻¹ h⁻¹ pri 400 °C in 5,5 MPa, medtem ko nepromoviran katalizator doseže pri enakih pogojih zgolj 158 mmol NH₃ gRu⁻¹ h⁻¹. Podoben trend je prav tako pri razgradnji, kjer je popolna pretvorba s promoviranim katalizatorjem pri 50 °C nižja kot pri nepromoviranem. Poskusi, kjer smo dinamično vklapljali in izklapljali izmenično magnetno polje, so pokazali doseganje stacionarnih stanj v približno 10-15 min. Kvantnomehanski izračuni in modeliranje mikrokinetike so pokazali, da stična površina med barijevim oksidom in rutenijem bistveno olajša hitrost določujočo stopnjo, ki je razklop N2, kar pojasni opaženo povečano aktivnost z barijem promoviranih katalizatorjev.
Aktivnost pripravljenih magnetnih katalizatorjev smo testirali tudi v šaržnem sistemu v procesih hidrogenacije tekočih organskih nosilcev vodika, in sicer na toluenu in dibenziltoluenu. Pri nizkem tlaku (1 MPa) in zmernih temperaturah (120–150 °C) smo dosegli visoke stopnje pretvorbe. Pri toluenu je bila 100-odstotna pretvorba dosežena že po dveh urah pri 120 °C, medtem ko je bil pri 150 °C za popolnoma hidrogeniranem dibenziltoluen dosežen izkoristek 37,6 % po 7,4 urah reakcije.
Disertacija uvaja nov koncept katalitskih procesov, ki temeljijo na magnetnem segrevanju katalitskega sloja. Ta inovativni pristop predstavlja izviren znanstveni prispevek, saj omogoča učinkovitejšo izrabo energije, hitrejši odziv sistema in odpira možnosti za razvoj prilagodljivih, nizkoogljičnih tehnologij, združljivih z obnovljivimi viri energije. Doseženi rezultati potrjujejo uporabnost razvitih materialov za dolgoročno shranjevanje energije v kemijski obliki in s tem pomembno prispevajo k trajnostnemu razvoju alternativnih tehnologij.
Keywords: magnetna kataliza, katalizator, elektrifikacija, amoniak, LOHC, obnovljivi viri energije
Published in DKUM: 23.12.2025; Views: 0; Downloads: 4
 Full text (8,66 MB) |
2. Green mechanochemical synthesis of binary and ternary cadmium chalcogenides with tunable band gapsMatjaž Kristl, Neža Zanjkovič, Jona Kunej, Sašo Gyergyek, Janja Stergar, 2025, original scientific article Abstract: In this work, we report on the mechanochemical preparation and characterization of binary (CdS, CdSe, and CdTe) and ternary (CdS0.5Se0.5, CdS0.5Te0.5, and CdSe0.5Te0.5) cadmium chalcogenides. The compounds were synthesized in a planetary micro mill using a zirconia grinding bowl and zirconia grinding balls. The products were examined by powder X-ray diffraction (pXRD), transmission electron microscopy (TEM), energydispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS), UV–Vis spectroscopy, and differential scanning calorimetry (DSC). Interestingly, CdO formed as a by-product only during milling of Cd+S and Cd+Se in air, while it was absent in the Cd+Te and all ternary systems. The materials were obtained in the form of irregularly shaped aggregates measuring up to several hundred nanometers, composed of nearly spherical primary nanoparticles with diameters in the 10–20 nm range. The band gap energies calculated using Tauc plots for CdS0.5Se0.5, CdS0.5Te0.5, and CdSe0.5Te0.5 were 2.01 eV, 1.72 eV, and 1.53 eV, respectively. These results demonstrate the expected tunability of band gaps in ternary cadmium chalcogenides and attest to the potential of such materials for semiconducting applications, particularly in solar cells. The mechanochemical approach is once again shown to be a simple and effective method for the preparation of both binary and ternary chalcogenides, avoiding the use of solvents, toxic precursors, and energy-consuming reaction conditions.
Keywords: cadmium, sulfide, selenide, telluride, ternary compounds, mechanochemistry, band gap
Published in DKUM: 01.12.2025; Views: 0; Downloads: 1
Full text (3,99 MB) |
3. New approach for adsorptive removal of the antibiotic ciprofloxacin: carboxymethyl-dextran-functionalised magnetic iron oxide nanomaterialsErik Mihelič, Lidija Fras Zemljič, Marjana Simonič, Sašo Gyergyek, Alenka Vesel, Silvo Hribernik, Matej Bračič, Ivan Anžel, Olivija Plohl, 2025, original scientific article Abstract: Antibiotic residues in environmental media pose a significant health, social and economic problem and require effective removal strategies. This study presents a novel approach for the removal of the antibiotic ciprofloxacin from water sources using magnetic iron oxide nanoparticles (MNPs) synthesised by co-precipitation, and subsequently functionalised with the polysaccharide carboxymethyl-dextran (CMD). The prepared nanoadsorbent was characterised extensively by various physicochemical analyses, to evaluate its morphology, crystal structure, surface chemistry, electrokinetic properties, thermogravimetric properties and magnetic features. These analyses confirmed the successful functionalisation of the MNPs with CMD highlighting its potential for effective adsorption applications. The stability of CMD coating on MNPs was evaluated in terms of total carbon content, an important, yet often overlooked factor. The adsorption performance of MNPs@CMD for ciprofloxacin was investigated systematically by studying the effects of adsorbent dosage, pH, initial ciprofloxacin concentration, ionic strength, adsorption time and kinetics, temperature, and reusability. Under optimal conditions, nanoadsorbent exhibited a satisfactory maximum adsorption capacity of 14.71 mg/g, and maintained a removal eff iciency of 79 % after four cycles, with minimal desorption of CMD layer on the MNPs. These findings demonstrate the potential of this magnetic polysaccharide nanoadsorbent for effective removal of ciprofloxacin from aqueous environments, enabling magnetic recovery and reuse.
Keywords: Carboxymethyl-dextran-MNPs, ciprofloxacin, adsorption
Published in DKUM: 26.05.2025; Views: 0; Downloads: 18
Full text (10,76 MB)
This document has many files! More... |
4. Razvoj magnetnih katalizatorjev na osnovi rutenija in njegovih zlitin za magnetno segrevano sintezo in razklop amonijakaŽiga Ponikvar, 2025, doctoral dissertation Abstract: Doktorsko delo predstavlja raziskave in izsledke na področju magnetno grete katalize za razklop in sintezo amonijaka. Magnetno gretje za namene katalize je relativno nov pristop, ki omogoča izredno hitro gretje katalizatorja brez fizičnega stika med indukcijsko tuljavo in ferimagnetnim ali feromagnetnim materialom v njeni notranjosti, ki se segreje v izmeničnem magnetnem polju (100–300 kHz). Brezkontaktni prenos energije in Joulovo gretje v električnem prevodniku zaradi induciranih vrtinčnih tokov je že uveljavljena tehnologija, trenutno v uporabi za kaljenje, taljenje, lotanje in varjenje kovinskih izdelkov. Zanimiv je tudi način izdelave z interferenčnim prileganjem sestavnih delov, kjer je potrebno segreti eno komponentno, da se razširi, nakar je vanjo mogoče vstaviti drugo. V redkih primerih lahko ta pristop uporabimo za gretje kovinskega medija znotraj reaktorja za katalizo. Za indukcijsko gretje prevodnika potrebujemo večje delce, vsaj nekaj mikronov, kar pa močno presega red velikosti zrn katalizatorja, ki morajo biti zaradi čim večje specifične površine majhna. V delu smo se osredotočili na razvoj nanostrukturnih materialov, ki so zmožni katalize in gretja po drugem mehanizmu sproščanja energije, na račun histereznih izgub v visokofrekvenčnem magnetnem polju, kar smo za namene naših raziskav poimenovali magnetno gretje.
Razvili smo več kompozitnih materialov, ki smo jih prilagodili trenutnim potrebam. Zaradi potrebe po dolgoročni stabilnosti katalizatorja v reduktivni atmosferi smo pripravili kompozit, ki sestoji iz magnetne podlage in katalitskih nanodelcev. Podlaga vsebuje feromagnetna jedra zlitine Co in Ni, ki tekom reakcije v reduktivnih pogojih ohranijo feromagnetne lastnosti, s spreminjanjem razmerja med kovinama pa vplivamo na lastnosti histerezne zanke in posledično sposobnosti gretja. Jedra so ukleščena v katalitsko podlago, γ-Al2O3 z veliko specifično površino (200 m2/g), ki preprečuje njihovo rast pri povišanih temperaturah in omogoča prenos toplote s feromagnetnih jeder do nanodelcev Ru, ki se nahajajo na njeni površini.
Opisani katalizator vsebuje dve vrsti nanodelcev. Feromagnetna zlitina CoNi omogoča gretje, Ru pa nudi katalitska mesta. Ker v literaturi nismo zasledili materialov, zmožnih hkratnega magnetnega gretja in katalize, smo razvili zlitino Ru in Co, s čemer smo želeli poenostaviti postopek priprave in omogočiti sproščanje toplote neposredno na katalitskem mestu. Bimetalni delci se najahajo na površini nemagnetnega γ-Al2O3, ki pa v tem primeru zgolj služi kot podlaga in ne omogoča gretja.
Rutenij je žlahtna kovina, ki katalizira razklop in tvorbo amonijaka, reakcija pa je ravnotežna. Amonijak je molekula z visoko vsebnostjo vodika, ker pa je transport vodika pri povišanem tlaku nevaren, se raziskujejo možnosti kemijske vezave. S katalitskim razklopom amonijaka pri povišani temperaturi lahko po potrebi proizvedemo vodik, sinteza amonijaka pa je eksotermna reakcija.
Za testiranje plinske katalize z magnetnim gretjem smo sestavili nov reaktorski sistem. V tuljavo indukcijskega ogrevalnika smo namestili cevko iz kremenovega stekla z magnetnim katalizatorjem, temperaturo pa smo spremljali z nemagnetnim termočlenom. Za preučevanje razklopa amonijaka smo uporabili razredčen amonijak pri sobnem tlaku, razpadne produkte in preostali amonijak pa smo spremljali s plinskim kromatografom in z masnim spektrometrom. Z bimetalnim katalizatorjem RuCo na nemagnetni podlagi smo pri 520 °C dosegli popolno pretvorbo 2,5 vol.% NH3 (40 mL/min). Z rutenijevim katalizatorjem na magnetnem γ-Al2O3 smo ugotovili, da je pri pretoku 30 mL/min 10 vol.% NH3 pretvorba popolna že pri 400 °C.
Za sintezo amonijaka smo uporabili vodik in dušik pri 30 bar ter enak rutenijev katalizator, saj je bil cilj pokazati reverzibilnost razvite tehnologije, ki jo usmerjamo z izbiro pogojev. Največji delež NH3 v efluentu in s tem najvišjo proizvodnost smo zaznali pri 550 °C (0,66 %), ki je z nadaljnjim dvigom temperature pričel upadati.
Keywords: Magnetna kataliza, razklop amonijaka, kompozitni katalizator, rutenij, nanodelci RuCo
Published in DKUM: 28.03.2025; Views: 0; Downloads: 59
Full text (11,28 MB) |
5. Functional coatings with ethyl cellulose-calcium carbonate alkaline nanoparticles for deacidification and mechanical reinforcement of paper artifactsMatej Bračič, Jasna Malešič, Mihael Brunčko, Doris Bračič, Alenka Ojstršek, Tea Kapun, Sašo Gyergyek, Karin Stana-Kleinschek, Tamilselvan Mohan, 2025, original scientific article Abstract: Paper artifacts susceptible to acid hydrolysis and mechanical stress require effective conservation methods to ensure their longevity. In this study, a novel approach for the deacidification of acidic paper using calcium carbonate (CaCO3) [1,2]-ethylcellulose nanoparticles (CaCO3-EC NPs) dispersed in a non-aqueous ethyl acetate solution is presented. The dispersions were carefully prepared and applied to model acidic paper samples using a dipcoating method and then analyzed for their effectiveness. Transmission electron microscopy showed the formation of agglomerates containing quadrangular alkaline nanoparticles with diameters of 40 to 100 nm and a total agglomerate size of 250 nm. Hydrodynamic analyzes indicate the presence of a swollen ethyl cellulose coating on these agglomerates, which facilitates their dispersion. The results show the effectiveness of the CaCO3-EC NPs system in neutralizing acidic components (change of paper pH from 4.3 to 7) due to the homogeneous distribution within the paper substrates, effectively arresting the degradation processes. Acid-base titration showed a linear correlation between the concentration of alkaline nanoparticles and the alkaline reserve, emphasizing the role of ethylcellulose in facilitating particle transport within the paper matrix. In addition, ethylcellulose was found to improve the mechanical properties of the treated paper, as demonstrated by the standard mechanical tests. Importantly, the optical properties remained unchanged after treatment, as no adverse changes in color were observed. These results underline the effectiveness of the developed deacidification dispersions for the treatment of acidic paper and potentially other cellulose-based cultural heritage documents prone to acidic degradation. This approach offers promising implications for preserving and restoring valuable historical materials.
Keywords: ethylcellulose, calcium carbonate, functional coating, deacidification, strengthening, cultural heritage
Published in DKUM: 20.03.2025; Views: 0; Downloads: 2
 Full text (184,18 KB)
This document has many files! More... |
6. Novel magnetic iron oxide-dextran sulphate nanocomposites as potential anticoagulants: Investigating interactions with blood components and assessing cytotoxicityOlivija Plohl, Lidija Fras Zemljič, Boštjan Vihar, Alenka Vesel, Sašo Gyergyek, Uroš Maver, Irena Ban, Matej Bračič, 2024, original scientific article Abstract: Examining the critical role of anticoagulants in medical practice, particularly their central function in preventing abnormal blood clotting, is of the utmost importance. However, the study of interactions between blood proteins and alternative anticoagulant nano-surfaces is still understood poorly. In this study, novel approach involving direct functionalisation of magnetic iron oxide nanoparticles (MNPs) as carriers with sulphated dextran (s-dext) is presented, with the aim of evaluating the potential of magnetically-responsive MNPs@s-dext as anticoagulants. The physicochemical characterisation of the synthesised MNPs@s-dext includes crystal structure analysis, morphology study, surface and electrokinetic properties, thermogravimetric analysis and magnetic properties` evaluation, which confirms the successful preparation of the nanocomposite with sulfonate groups. The anticoagulant potential of MNPs@s-dext was investigated using a standardised activated partial thromboplastin time (APTT) test and a modified APTT test with a quartz crystal microbalance with dissipation (QCM-D) which confirmed the anticoagulant effect. Time-resolved solid-liquid interactions between the MNPs@s-dext and model blood proteins bovine serum albumin and fibrinogen were also investigated, to gain insight into their hemocompatibility, and revealed protein-repellence of MNPs@s-dext against blood proteins. The study also addressed comprehensive cytotoxicity studies of prepared nanocomposites, and provided valuable insights into potential applicability of MNPs@s-dext as a promising magnetic anticoagulant in biomedical contexts.
Keywords: dextran sulphate, magnetic nanoparticles, blood protein interactions, clot formation, anticoagulants, cytotoxicity studies
Published in DKUM: 25.07.2024; Views: 107; Downloads: 44
Full text (892,02 KB)
This document has many files! More... |
7. Selection on antimony-doped tin oxide (ATO) as an efficient support for iridium-based oxygen evolution reaction (OER) catalyst in acidic mediaIkhlas Ahmad Khan, Per Morgen, Sašo Gyergyek, Raghunandan Sharma, Shuang Ma Andersen, 2023, original scientific article Abstract: Reducing the iridium content while preserving high OER activity is an important prerequisite for the progress of inexpensive anodic water splitting electrocatalysts in low pH medium. Here we report the effects of bulk and surface structures of antimony doped tin oxide (ATO) supports on the ATO supported Ir-based electrocatalyst’s activity for oxygen evolution reaction (OER) in acidic media. Ability of the ATO supports to anchor the Ir nanoparticles, measured as the fraction of Ir species from reaction bath landed on ATO support (conversion efficiency; η c ), is found to be strongly dependent on its surface chemistry, characterized in terms of presence of surface oxygen groups (O surface ). Both O surface content and electronic conductivity of ATOs show strong influence on OER activity. In general, high conductivity and low O surface though low O surface may compromise η c content are preferred for high OER activity, . The optimal catalyst demonstrates superior OER activity of 777 A g 1 , 2.5 times that of the state-of-the-art commercial catalyst at 1.65 V vs. RHE. Further, the synthesized catalysts exhibit durability comparable to that of the commercial counterpart.
Published in DKUM: 08.05.2024; Views: 137; Downloads: 51
Full text (4,13 MB)
This document has many files! More... |
8. |
9. Microwave Synthesis of Poly(Acrylic) Acid-Coated Magnetic Nanoparticles as Draw Solutes in Forward OsmosisSabina Vohl, Irena Ban, Mihael Drofenik, Hermina Bukšek, Sašo Gyergyek, Irena Petrinić, Claus Hélix-Nielsen, Janja Stergar, 2023, original scientific article Abstract: Polyacrylic acid (PAA)-coated magnetic nanoparticles (MNP@PAA) were synthesized and evaluated as draw solutes in the forward osmosis (FO) process. MNP@PAA were synthesized by microwave irradiation and chemical co-precipitation from aqueous solutions of Fe2+ and Fe3+ salts. The results showed that the synthesized MNPs have spherical shapes of maghemite Fe2O3 and superparamagnetic properties, which allow draw solution (DS) recovery using an external magnetic field. Synthesized MNP, coated with PAA, yielded an osmotic pressure of ~12.8 bar at a 0.7% concentration, resulting in an initial water flux of 8.1 LMH. The MNP@PAA particles were captured by an external magnetic field, rinsed in ethanol, and re-concentrated as DS in repetitive FO experiments with deionized water as a feed solution (FS). The osmotic pressure of the re-concentrated DS was 4.1 bar at a 0.35% concentration, resulting in an initial water flux of 2.1 LMH. Taken together, the results show the feasibility of using MNP@PAA particles as draw solutes.
Keywords: magnetic nanoparticles, microwave synthesis, polyacrilic acid, osmotic pressure, draw solution, forward osmosis
Published in DKUM: 05.12.2023; Views: 433; Downloads: 22
Full text (3,00 MB)
This document has many files! More... |
10. Synthesis of magnetic nanoparticles with covalently bonded polyacrylic acid for use as forward osmosis draw agentsIrena Ban, Mihael Drofenik, Hermina Bukšek, Irena Petrinić, Claus Hélix-Nielsen, Sabina Vohl, Sašo Gyergyek, Janja Stergar, 2023, original scientific article Abstract: Multicoated magnetite (Fe3O4) magnetic nanoparticles (MNPs) with polyacrylic acid (PAA) as a terminal hydrophilic ligand were synthesized and examined for use as a draw solution (DS) agent in forward osmosis (FO). After coating superparamagnetic iron-oxide MNPs with (3-aminopropyl)triethoxysilane (APTES) the carboxyl groups of PAA were bound to APTES amino groups via the crosslinker 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) forming a peptide bond resulting in stable water-soluble particles (MNP@APTES@PAA) with a concentration-normalised osmotic pressure of 1.56 bar L g−1. The MNP@APTES@PAA solution was evaluated as a DS in two FO filtrations with deionized (DI) water as a feed solution (FS): one using freshly prepared MNP@APTES@PAA and one using magnetically recovered (re-concentrated) MNP@APTES@PAA. The resulting MNP@APTES@PAA nanocomposites exhibit good colloidal stability in aqueous solution with a concentration-normalized osmotic pressure of 1.56 bar L g−1. This is 12-fold higher than that in our previous studies of poly-sodium-acrylate coated MNPs and 3-fold higher than that of citric acid coated MNPs. The water recoveries of the two filtrations were 25.7% and 13.6%, respectively, after 2 h of FO filtration time resulting in a DS osmotic pressure of 2.5 bar with a concentration of 4.3 g L−1 and a DS osmotic pressure of 2.6 with a concentration of 3.7 g L−1 respectively.
Keywords: magnetic nanoparticle, forward osmosis, draw solution, osmose
Published in DKUM: 16.08.2023; Views: 424; Downloads: 16
Full text (1,92 MB)
This document has many files! More... |
