1. Advancing oxygen evolution catalysis with dual-phase nickel sulfide nanostructuresNeelakandan Marath Santhosh, Suraj Gupta, Vasyl Shvalya, Martin Košiček, Janez Zavašnik, Uroš Cvelbar, 2024, izvirni znanstveni članek Povzetek: The production, conversion and storage of energy based on electrocatalysis, mainly assisted by oxygen evolution reaction (OER), plays a crucial role in alkaline water electrolyzers (AWEs) and fuel cells. Nevertheless, the insufficient availability of highly efficient catalyst materials at a reasonable cost that overcome the sluggish electrochemical kinetics of the OER is one of the significant obstacles. Herein, we report a fast and facile synthesis of vapor phase deposition of dual-phase nickel sulfide (Ni-sulfide) using low-temperature annealing in the presence of H2S and demonstrated as an efficient catalyst for OER to address the issues with sluggish electrochemical kinetics. The dual-phase Ni-sulfide structures consist of densely packed 10–50 μm microcrystals with 40–50 individual dual-phase layers, such as NiS and Ni7S6. As an electrocatalyst, the dual-phase Ni-sulfide exhibits excellent OER activity by achieving a current density of 10 mA/cm2 at an overpotential (η10) of 0.29 V and excellent electrochemical stability over 50 h. Besides, the Ni-sulfide displays considerable electrochemical robustness in alkaline conditions and forms OER-active Ni-oxide/hydroxide species during the process. Using an energy-efficient synthesis method, the fabricated unique crystalline nanodesign of dual-phase Ni-sulfide could open new pathways for the controlled synthesis of a high-efficiency group of electrocatalysts for a long-time stable electrochemical catalytic activity.
Ključne besede: electrocatalysts
Objavljeno v DiRROS: 17.01.2025; Ogledov: 48; Prenosov: 15
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2. Light-assisted catalysis and the dynamic nature of surface species in the reverse water gas shift reaction over ▫$Cu/\gamma-Al_2O_3$▫Kristijan Lorber, Iztok Arčon, Matej Huš, Janez Zavašnik, Jordi Sancho-Parramon, Anže Prašnikar, Blaž Likozar, Nataša Novak Tušar, Petar Djinović, 2024, izvirni znanstveni članek Povzetek: The reverse water gas shift (RWGS) reaction converts CO2 and H2 into CO and water. We investigated Cu/γ-Al2O3 catalysts in both thermally driven and light-assisted RWGS reactions using visible light. When driven by combined visible light and thermal energy, the CO2 conversion rates were lower than in the dark. Light-assisted reactions showed an increase in the apparent activation energy from 68 to 87 kJ/mol, indicating that light disrupts the energetically favorable pathway active in the dark. A linear correlation between irradiance and decreasing reaction rate suggests a photon-driven phenomenon. In situ diffuse reflectance infrared Fourier transform spectroscopy and TD-DFT analyses revealed that catalyst illumination causes significant, partly irreversible surface dehydroxylation, highlighting the importance of OH groups in the most favorable RWGS pathway. This study offers a novel approach to manipulate surface species and control activity in the RWGS reaction.
Objavljeno v DiRROS: 19.12.2024; Ogledov: 129; Prenosov: 71
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3. Novel ▫$TiO_2$▫-supported gold nanoflowers for efficient photocatalytic ▫$NO_x$▫ abatementŠpela Slapničar, Gregor Žerjav, Janez Zavašnik, Matevž Roškarič, Matjaž Finšgar, Albin Pintar, 2024, izvirni znanstveni članek Povzetek: t: In this study, we pioneered the synthesis of nanoflower-shaped TiO2 -supported Au photocatalysts and investigated their properties. Au nanoflowers (Au NFs) were prepared by a Na-citrate and hydroquinone-based preparation method, followed by wet impregnation of the derived Au NFs on the surface of TiO2 nanorods (TNR). A uniform and homogeneous distribution of Au NFs was observed in the TNR + NF(0.7) sample (lower Na-citrate concentration), while their distribution was heterogeneous in the TNR + NF(1.4) sample (higher Na-citrate concentration). The UV-Vis DR spectra revealed the size- and shape-dependent optical properties of the Au NFs, with the LSPR effect observed in the visible region. The solid-state EPR spectra showed the presence of Ti3+, oxygen vacancies and electron interactions with organic compounds on the catalyst surface. In the case of the TNR + NF(0.7) sample, high photocatalytic activity was observed in the H2 -assisted reduction of NO2 to N2 at room temperature under visible-light illumination. In contrast, the TNR + NF(1.4) catalyst as well as the heat-treated samples showed no ability to reduce NO2 under visible light, indicating the presence of deformed Au NFs limiting the LSPR effect. These results emphasized the importance of the choice of synthesis method, as this could strongly influence the photocatalytic activity of the Au NFs
Objavljeno v DiRROS: 25.07.2024; Ogledov: 379; Prenosov: 275
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4. Selective glucose oxidation to glucaric acid using bimetallic catalysts : lattice expansion or electronic structure effect?Žan Lavrič, Janvit Teržan, Ana Kroflič, Janez Zavašnik, Joanna E. Olszówka, Štefan Vajda, Matej Huš, Miha Grilc, Blaž Likozar, 2024, izvirni znanstveni članek Povzetek: Our study presents a comprehensive approach for the selective oxidation of glucose to glucaric acid (GA) by heterogeneous catalysis. We have synthesized and characterized Au/ZrO2, AuCu/ZrO2 and AuPt/ZrO2 catalysts using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and oxygen pulse chemisorption (OPS) techniques. Combining experimental observations with in-depth density functional theory (DFT) studies, we found that bimetallic catalysts form alloys, which exhibit different characteristics than monometallic counterparts for the given reaction. We performed batch reactions, varying temperature and oxygen pressure, and used the data to construct a predictive microkinetic model. As it turned out, AuPt/ZrO2 showed the highest selectivity, yielding 32 % of GA at 100 °C and 30 barg O2. Our results provide valuable insights for the developing of efficient catalysts and point out the bottlenecks for the oxidation of glucose to GA.
Ključne besede: glucaric acid, glucose oxidation, catalyst characterization, density functional theory, microkinetic modelling
Objavljeno v DiRROS: 06.12.2023; Ogledov: 779; Prenosov: 334
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5. Optimization method based on simplex for surface area improved photocatalytic performance of ▫$g-C_3N_4$▫Matevž Roškarič, Janez Zavašnik, Dániel Dániel Zámbó, Tomaž Kotnik, Sebastijan Kovačič, Gregor Žerjav, Albin Pintar, 2023, izvirni znanstveni članek Povzetek: The main objective of the present study was to increase the specific surface area (SBET) of graphitic carbon nitride (g-C3N4) prepared from dicyandiamide by effectively modifying the synthesis procedure using the Simplex optimization method. A remarkable increase in SBET was achieved in only a few steps, with the highest value of 86 m2/g. Compared to the reference material, the improved photocatalyst exhibited enhanced and unique structural, textural, optical, and electronic properties, reflected in the improved ability of the photocatalyst to degrade a variety of organic pollutants dissolved in water. By performing scavenger and spin-trapping experiments, it was confirmed that the major reactive oxygen species formed under visible-light illumination of the enhanced photocatalyst were singlet oxygen (1O2) and superoxide anion radicals (O2–•) with a purposed formation mechanism. The enhanced formation of 1O2 enabled high activity and stability of the optimized materials as well as selective response to degradation of the pharmaceutical compounds studied. By using the simple and fast Simplex optimization algorithm to determine new synthesis parameters, we obtained an improved g-C3N4 that completely degrades bisphenol A under the conditions studied.
Objavljeno v DiRROS: 08.11.2023; Ogledov: 718; Prenosov: 330
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6. Photo, thermal and photothermal activity of ▫$TiO_2$▫ supported Pt catalysts for plasmon-driven environmental applicationsGregor Žerjav, Zafer Say, Janez Zavašnik, Matjaž Finšgar, Christoph Langhammer, Albin Pintar, 2023, izvirni znanstveni članek Povzetek: TiO2+Pt plasmonic solids with 1 wt% Pt and different TiO2 supports (anatase nanoparticles (TNP), polycrystalline nanorods (a-TNR) and single-crystal anatase nanorods (TNR)) were synthesized using the wet impregnation technique and tested as photo, thermal and photothermal catalysts in gas-solid and gas-liquid-solid reactions. Due to the different charges of the TiO2 support surfaces, Pt particles with different sizes, crystallinities and degrees of interaction with the TiO2 supports were formed during the synthesis. The heights of the Schottky barrier (SBH) were 0.38 eV for the a-TNR+Pt, 0.41 eV for the TNP+Pt, and 0.50 eV for the TNR+Pt samples, respectively. The low visible-light-triggered photocatalytic activity of the TNR+Pt catalyst toward the oxidation of water-dissolved bisphenol A (BPA) is attributed to its high SBH and active site deactivation due to the adsorption of BPA and/or BPA oxidation products. The highest photothermal catalytic H2-assisted NO2 reduction rate was expressed by the TNR+Pt catalyst. This can be ascribed to the presence of a narrow particle size distribution of small Pt particles, the absence of the Pt catalysed reduction of the TNR support at higher temperatures, and the lower rate of re-injection of “hot electrons” from the TNR support to the Pt particles.
Ključne besede: heterogeneous photocatalysis, titanium dioxide, plasmonic noble metal, platinum particles, visible light illumination, Schottky barrier height, bisphenol A, wastewater treatment, NOx abatement, air cleaning, microreactor, thermal catalysis, photothermal catalysis
Objavljeno v DiRROS: 23.06.2023; Ogledov: 946; Prenosov: 488
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7. Synthesis and characterization of plasmonic ▫$Au/TiO_2$▫ nanorod solids for heterogeneous photocatalysisŠpela Slapničar, Gregor Žerjav, Janez Zavašnik, Matjaž Finšgar, Albin Pintar, 2023, izvirni znanstveni članek Povzetek: Plasmonic Au (1 wt%) catalysts deposited on hydrothermally synthesized TiO2 nanorods (TNR) were investigated in this study. Based on the duration of mixing of the Au precursor/TNR suspension during the wet impregnation synthesis and parameters of the end calcination, Au/TiO2 catalysts with different sizes of Au nanoparticles (Au NPs) were obtained. The prepared solids were thoroughly characterized by several instrumental techniques to investigate property-activity relationships. Regardless of the size of Au particles on the catalyst surface, an absorption peak at 550 nm occurred in all UV-Vis diffuse reflectance spectra of the investigated Au/TiO2 catalysts, which is characteristic of the localized surface plasmon resonance effect exerted by metallic Au NPs. By measuring the formation of reactive oxygen species under visible-light illumination using various scavengers, the production of superoxide anion radicals (O2•single bond) and hydroxyl radicals were identified, however, the former were found to represent the main reactive oxygen species that govern the oxidation of aqueous bisphenol A (BPA) employed as a model organic pollutant. The activity of Au/TiO2 catalysts for the generation of O2•single bond radicals (and BPA oxidation) increases by increasing the Schottky barrier height, which is due to the slow reduction of water-dissolved O2 on the catalyst surface.
Ključne besede: heterogeneous photocatalysis, titanate nanorods, gold nanoparticles, wet impregnation, localized surface plasmon resonance effect
Objavljeno v DiRROS: 26.04.2023; Ogledov: 1190; Prenosov: 499
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8. Influence of the calcination duration of ▫$g-C_3N_4/TiO_2$▫ veggie-toast-like photocatalyst on the visible-light triggered photocatalytic oxidation of bisphenol AMatevž Roškarič, Gregor Žerjav, Matjaž Finšgar, Janez Zavašnik, Albin Pintar, 2023, izvirni znanstveni članek Povzetek: Two commercially available TiO2 (hexagonal-like and spherical-like particles) were used to investigate the effect of g-C3N4 “melting” on the photocatalytic properties of g-C3N4/TiO2 composites. Improvement in the contact between the components was observed when they were thermally treated at 350 °C for an extended period of time (between 2 and 72 h) due to the partial melting and phase fusion of g-C3N4. Consequently, the enhanced contact between the phases allows easier injection of photogenerated electrons from the conduction band of g-C3N4 into TiO2, improving charge carrier separation. The prepared composites were tested for bisphenol A degradation under visible-light illumination, which showed that the components that had been calcined for 24 h performed better due to the improved charge carrier separation. Superoxide anionic radicals and photogenerated holes were identified as active species in the photooxidation experiments conducted under visible-light illumination.
Ključne besede: titanium dioxide, photocatalyst, calcination time, photocatalysis under visible-light illumination, water remediation, bisphenol A
Objavljeno v DiRROS: 17.03.2023; Ogledov: 1172; Prenosov: 529
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9. Correlations between the catalyst properties and catalytic activity of Au on ▫$ZrO_2-CeO_2$▫ in the hydrogenation of ▫$CO_2$▫Hue-Tong Vu, Matjaž Finšgar, Janez Zavašnik, Nataša Novak Tušar, Albin Pintar, 2023, izvirni znanstveni članek Ključne besede: ▫$CO_2$▫ utilization, gold, mixed oxides, amorphous ▫$ZrO_2$▫, methanol synthesis
Objavljeno v DiRROS: 16.03.2023; Ogledov: 1506; Prenosov: 597
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