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Removal of manganese in batch and fluidized bed systems using beads of zeolite a as adsorbent
Bojana Obradovic, Nataša Novak Tušar, Iztok Arčon, Janez Kovač, Mina Jovanovic, Nevenka Rajić, 2016, izvirni znanstveni članek

Opis: In this study the uptake capacity of Mn(II) ions by zeolite A beads was investigated for different initial Mn concentration (100e400 mg Mn dm^-3) in batch mode at 25e55 C. The obtained adsorption capacity varying from 30 to 50 mg Mn g^-1 demonstrated a high affinity of zeolite A towards Mn(II) present in solutions. Kinetic studies indicated the intra-particle diffusion as the rate limiting step up to 45 C with apparent diffusivities in the range (1.2e2.0) x 10^-13 m2 s^-1 and the activation energy of 21.9 kJ mol^-1, which implies strong interactions between the zeolite A and Mn ions. At 55 C ion-exchange became the rate limiting step. The adsorption isotherms were studied at 25 C showing that the Mn adsorption is the best described by the Langmuir model suggesting a homogenous zeolite surface. XPS analysis of the Mnloaded beads showed that there is no surface accumulation of Mn but an almost uniform Mn distribution inside zeolite A, whereas XANES and EXAFS suggested that the adsorption of Mn(II) was followed by the Mn(II) oxidation and oxide formation. Regeneration of the spent zeolite was examined in 8 adsorption/desorption cycles by a chelating Na2EDTA in a fluidized column. It has been found that zeolite A beads could be reused for at least 4 cycles with satisfactory Mn(II) adsorption efficiencies of about 70%.
Najdeno v: osebi
Ključne besede: Zeolite A Manganese Adsorption kinetics EXAFS/XANES XPS
Objavljeno: 01.04.2016; Ogledov: 3985; Prenosov: 0
.pdf Polno besedilo (1,27 MB)

Photocatalytic Activity of Zirconium- and Manganese- Codoped Titania in Aqueous Media: The Role of the Metal Dopant and its Incorporation Site
Nataša Novak Tušar, Iztok Arčon, O. L. Pliekhov, Urška Lavrenčič Štangar, 2016, izvirni znanstveni članek

Opis: The development of efficient TiO2-based photocatalysts for water treatment is mainly performed by doping with transition metals or by establishing junctions between different phases, metal–semiconductor or semiconductor–semiconductor. We present, for the first time, the synthesis of Zr- and Mn-modified TiO2 by a redesigned sol–gel technique that allows the formation of heterometallic bridges on the TiO2 surface. Cations of the doping metals are located in the pores of mesoporous anatase and attached to the crystalline TiO2 walls. The presence of the Zr enhances the photoactivity of the TiO2 catalyst. However, the introduction of Mn decreases the photocatalytic efficiency in a nonadditive manner. The inhibition effect was assigned to the side reaction between hydroxyl radicals and Mn ions. The fact that Mn effectively scavenges the hydroxyl radicals and, consequently, inhibits the whole oxidation process is direct proof that hydroxyl radicals are the main reactive species in the photocatalytic oxidative processes on TiO2 surfaces in aqueous media and the process of COH generation is the rate-determining step, which was confirmed using a method based on the decolorization of a commercial dye Bezaktiv Blau in a reaction with Fenton’s reagent as a source of hydroxyl radicals.
Najdeno v: osebi
Ključne besede: doping, manganese, oxidation, X-ray absorption spectroscopy, zirconium
Objavljeno: 21.07.2016; Ogledov: 3032; Prenosov: 0
.pdf Polno besedilo (577,49 KB)

Role of Surface Cu-O-Zr Sites in the Photocatalytic Activity of TiO2 Nanoscale Particles
Nataša Novak Tušar, Iztok Arčon, Urška Lavrenčič Štangar, Olena Pliekhova, 2016, objavljeni povzetek znanstvenega prispevka na konferenci

Najdeno v: osebi
Ključne besede: Photocatalysis, Titanium dioxide, Copper, Zirconia, co-doping, EXAFS, XANES
Objavljeno: 23.08.2017; Ogledov: 3364; Prenosov: 0
.pdf Polno besedilo (426,28 KB)

Contribution of Cu and Zr to the Properties of TiO2 for Photocatalytic Water Treatment
Olena Pliekhova, Iztok Arčon, Nataša Novak Tušar, Urška Lavrenčič Štangar, 2017, objavljeni povzetek znanstvenega prispevka na konferenci

Najdeno v: osebi
Ključne besede: Photocatalysis, water treatment, surface modification, durability
Objavljeno: 23.08.2017; Ogledov: 3260; Prenosov: 0
.pdf Polno besedilo (509,62 KB)

Surface modified titanium dioxide using transition metals
Andraž Šuligoj, Iztok Arčon, Matjaž Mazaj, Goran Dražić, Denis Arčon, Pegie Cool, Urška Lavrenčič Štangar, Nataša Novak Tušar, 2018, izvirni znanstveni članek

Opis: Titanium dioxide has been widely used as an antimicrobial agent, UV-filter and catalyst for pollution abatement. Herein, surface modifications with selected transition metals (Me) over colloidal TiO2 nanoparticles and immobilization with a colloidal SiO2 binder as composite films (MeTiO2/SiO2) on a glass carrier were used to enhance solar-light photoactivity. Colloidal TiO2 nanoparticles were modified by loading selected transition metals (Me ¼ Mn, Fe, Co, Ni, Cu, and Zn) in the form of chlorides on their surface. They were present primarily as oxo-nanoclusters and a portion as metal oxides. The structural characteristics of bare TiO2 were preserved up to an optimal metal loading of 0.5 wt%. We have shown in situ that metal-oxo-nanoclusters with a redox potential close to that of O2/O2 were able to function as co-catalysts on the TiO2 surface which was excited by solar-light irradiation. The materials were tested for photocatalytic activity by two opposite methods; one detecting O2 (reduction, Rz ink test) while the other detecting OH (oxidation, terephthalic acid test). It was shown that the enhancement of the solar-light activity of TiO2 by the deposition of transition metal oxo-nanoclusters on the surface depends strongly on the combination of the reduction potential of such species and appropriate band positions of their oxides. The latter prevented excessive self-recombination of the photogenerated charge carriers by the nanoclusters in Ni and Zn modification, which was probably the case in other metal modifications. Overall, only Ni modification had a positive effect on solar photoactivity in both oxidation and reduction reactions.
Najdeno v: osebi
Ključne besede: surface modified TiO2, XANES, EXAFS, Nickel, solar light photocatalyst
Objavljeno: 01.06.2018; Ogledov: 2330; Prenosov: 0
.pdf Polno besedilo (1,24 MB)

The effect of Zr loading on photocatalytic activity of Cu modified TiO2
Urška Lavrenčič Štangar, Nataša Novak Tušar, O. L. Pliekhov, Mattia Fanetti, Iztok Arčon, Olena Pliekhova, 2018, objavljeni znanstveni prispevek na konferenci

Najdeno v: osebi
Ključne besede: Titanium diokside, acidic sites, surface titration, copper, zirconium
Objavljeno: 10.09.2018; Ogledov: 2566; Prenosov: 0
.pdf Polno besedilo (39,79 MB)

The effect of Zr loading on photocatalytic activity of Cu modified TiO [sub] 2
Urška Lavrenčič Štangar, Nataša Novak Tušar, Iztok Arčon, Mattia Fanetti, O. L. Pliekhov, Olena Pliekhova, 2018, objavljeni povzetek znanstvenega prispevka na konferenci

Najdeno v: osebi
Ključne besede: Cu Zr modified TiO2, EXAFS, XANES
Objavljeno: 12.09.2018; Ogledov: 2254; Prenosov: 0
.pdf Polno besedilo (990,75 KB)

Cu and Zr surface sites in photocatalytic activity of TiO [sub] 2 nanoparticles
Olena Pliekhova, O. L. Pliekhov, Mattia Fanetti, Iztok Arčon, Nataša Novak Tušar, Urška Lavrenčič Štangar, 2019, izvirni znanstveni članek

Opis: The present work is focused on the role of ZrO2 modification in the performance of CuO modified TiO2. Zirconia loading leads to formation of more resistant photocatalytic layers compared to samples modified with only copper containing species. Surface modification of mixed phase TiO2 with CuO/ZrO2 improves the degradation of Reactive blue 19 dye under simulated solar irradiation. An in-depth investigation of the catalysts showed that in case of CuO/ZrO2 modification, the covering of the TiO2 surface with zirconium containing species prevents morphological and harmful energetic changes induced by copper species formed on the rutile TiO2 phase at a higher copper loading.
Najdeno v: osebi
Ključne besede: titanium dioxide, surface modification, XAS analysis, surface acidity, Hammett indicators
Objavljeno: 26.03.2019; Ogledov: 2124; Prenosov: 0
.pdf Polno besedilo (996,21 KB)

New Insights into Manganese Local Environment in MnS-1Nanocrystals
Alenka Ristić, Matjaž Mazaj, Iztok Arčon, Nina Daneu, Nataša Zabukovec Logar, Roger Glaser, Nataša Novak Tušar, 2019, izvirni znanstveni članek

Opis: Manganese plays an important role in redox catalysis using zeolites as inorganic support materials, but the formation of the preferred redox manganese species (framework or extraframework) is still not well understood. Herein, the influence of the amount of manganese together with conventional and microwave-assisted hydrothermal synthesis paths on the formation of manganese species within the zeolite silicalite-1 (S-1) with MFI structure was investigated. It was found out that both synthesis procedures led to the formation of framework and extraframework manganese species, but in different molar ratios. However, the conventional synthesis procedure with all Mn/Si molar ratios generates more framework Mn in comparison to the microwave procedure. Additionally, the diminution of the zeolite crystals to nanoscale from 100 to 200 nm was achieved via the conventional procedure for the first time. UV–vis, Raman, and X-ray absorption spectroscopic analyses revealed different local environments of manganese: Mn3+ incorporated into the silicalite-1 framework as “framework manganese” and Mn2+/3+ present as “extraframework manganese” (Mn2O3, Mn3O4). TEM reveals the presence of Mn3O4 nanorods. Both framework manganese and extraframework manganese exhibit good catalytic activity for styrene epoxidation. Catalytic results suggest that, in oxidation reactions of hydrocarbons, framework manganese is more active at lower Mn contents (Mn/Si < 0.015), whereas extraframework manganese is more active at higher loadings (Mn/Si > 0.015).
Najdeno v: osebi
Ključne besede: MnS-1 Nanocrystals, Mn XANES, EXAFS, zeolites, microwave-assisted hydrothermal synthesis
Objavljeno: 06.05.2019; Ogledov: 2221; Prenosov: 0
.pdf Polno besedilo (9,33 MB)

In-depth structural characterization and magnetic properties ofquaternary ferrite systems Co0.5Zn0.25M0.25Fe2O4(M¼Ni, Cu, Mn, Mg)
Nataša Novak Tušar, Myrjam Mertens, Aurel Pui, Iztok Arčon, Radu-G. Ciocarlan, Elena M. Seftel, Pegie Cool, 2019, izvirni znanstveni članek

Opis: This paper investigates the structural and magnetic properties of a mixed series of ferrites having generalformula Co0.5Zn0.25M0.25Fe2O4(M¼Ni, Cu, Mn, Mg). Insights on surface chemistry, structural andmorphological parameters are presented in order to achieve highly tuned ferrite systems with specificcharacteristics. The site occupancy of the cations in the spinel structure was determined using XAS, XRDand Raman spectroscopy. A 100% occupancy of the tetrahedral sites was observed for the Zn cations forall the samples. Co cations occupied the octahedral sites in proportion of 100% for CoeZneCu, CoeZneMg and around 80% for CoeZneNi, CoeZneMn. Ni cations were found only in the octahedral sites,while Cu 80% in the octahedral sites and Mn 60% in the octahedral sites. The cation distribution resultswere correlated with the magnetic properties data. At the same time, not only the cation distribution, butalso the particles size distribution was observed to have a great influence on magnetic and opticalproperties of the ferrites. Given the importance of the surface chemistry of the nanoparticles, XPS and FT-IR analysis were used to prove the functionalization with groups belonging to the surfactant. Moreover,the peculiar behavior of manganese in spinel structures was clarified and the origin of the multiple states(Mn2þand Mn4þ) was elucidated. Finally, parallels have been drawn between the use of different cationsin mixed ferrites in order to gain specific properties.
Najdeno v: osebi
Ključne besede: FerritesMagnetic propertiesSpinel nanoparticlesX-ray absorption spectroscopyCo-precipitation
Objavljeno: 23.10.2019; Ogledov: 2036; Prenosov: 0
.pdf Polno besedilo (2,11 MB)

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