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11.
Improved photocatalytic activity of SnO[sub]2-TiO[sub]2 nanocomposite thin films prepared by low-temperature sol-gel method
Ksenija Maver, Iztok Arčon, Mattia Fanetti, Samar Al Jitan, Giovanni Palmisano, Matjaž Valant, Urška Lavrenčič Štangar, 2021, izvirni znanstveni članek

Opis: The objective of this research was to investigate how the photocatalytic activity of pure TiO2 can be improved by SnO2 modification. Different molar ratios of tin to titanium were prepared. The correlation between tin concentration and structural properties was investigated to explain the mechanism of photocatalytic efficiency and to optimize the synthesis conditions to obtain enhanced activity of the SnO2-modified TiO2 photocatalysts under UV-irradiation. The SnO2-modified TiO2 photocatalysts were prepared by a low-temperature sol-gel method based on organic tin and titanium precursors. The precursors underwent sol-gel reactions separately to form SnO2-TiO2 sol. The sol-gels were deposited on a glass substrate by a dip-coating technique and dried at 150 ◦C to obtain the photocatalysts in the form of a thin film. To test the thermal stability of the material, an additional set of photocatalysts was prepared by calcining the dried samples in air at 500 ◦C. The photocatalytic activity of the samples was determined by measuring the degradation rate of an azo dye. An increase of up to 30% in the photocatalytic activity of the air-dried samples was obtained when the TiO2 was modified with the SnO2 in a concentration range of 0.1–1 mol.%. At higher SnO2 loadings, the photocatalytic activity of the photocatalyst was reduced compared to the unmodified TiO2. The calcined samples showed an overall reduced photocatalytic activity compared to the air-dried samples. Various characterization techniques (UV-Vis, XRD, N2-physisorption, TEM, EDX, SEM, XAS and photoelectrochemical characterization) were used to explain the mechanism for the enhanced and hindered photocatalytic performances of the SnO2-modified TiO2 photocatalysts. The results showed that the nanocrystalline cassiterite SnO2 is attached to the TiO2 nanocrystallites through the Sn-O-Ti bonds. In this way, the coupling of two semiconductors, SnO2 and TiO2, was demonstrated. Compared to single-phase photocatalysts, the coupling of semiconductors has a beneficial effect on the separation of charge carriers, which prolongs their lifetime for accessibility to participate in the redox reactions. The maximum increase in activity of the thin films was achieved in the low concentration range (0.1–1 mol.%), which means that an optimal ratio and contact of the two phases is achieved for the given physical parameters such as particle size, shape and specific surface area of the catalyst.
Ključne besede: photocatalytic activity, Sn-modified TiO2, low-temperature, thin films, XAS analysis
Objavljeno v RUNG: 05.07.2021; Ogledov: 2584; Prenosov: 0
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12.
Structural, morphological and chemical properties of metal/topological insulator interfaces : dissertation
Katja Ferfolja, 2021, doktorska disertacija

Opis: Topological insulators (TIs) represent a new state of matter that possess a different band structure than regular insulators or conductors. They are characterized with a band gap in the bulk and conductive topological states on the surface, which are spin polarized and robust toward contamination or deformation of the surface. Since the intriguing properties of the TIs are localized at the surface, it is important to obtain knowledge of the possible phenomena happening at the interface between TIs and other materials. This is especially true in the case of metals, due to the fact that such interfaces will be present in the majority of foreseen TI applications. The presented study combines microscopy and spectroscopy techniques for characterization of morphology, stability and chemical interaction at the interface between TI and metals deposited by means of physical vapor deposition. Our research is based on the interface of Bi2Se3 topological insulator with Ag, Ti and Pt – metals that can be encountered in devices or applications predicted to utilize the special properties of topological insulators. STM and SEM imaging of Ag/Bi2Se3 interface showed that Ag atoms arrange on the surface in the form of islands, whereas significantly bigger agglomerates are found at the surface steps. The interface was found to be unstable in time and resulted in the absorption of the metal into the crystal at room temperature. Evidences of a chemical reaction at the Ag/Bi2Se3 interface are presented, showing that new phases (Ag2Se, AgBiSe2 and metallic Bi) are formed. Deposition of Ti on Bi2Se3 resulted in different morphologies depending on the film thickness. At a very low coverage (<1 Å) islands are formed. However, the islands growth is hindered before the completion of a full layer due to the occurrence of a chemical reaction. No surface features could be detected by SEM for Ti coverage up to 20 nm. In contrary, when Ti thickness reached 40 nm, compressive stress triggered buckling of the deposited film. XPS analysis revealed that a redox solid-state reaction occurs at the Ti/Bi2Se3 interface at room temperature forming titanium selenides and metallic Bi. The reaction has significant kinetics even at cryogenic temperature of 130 K. Pt forms a homogenous film over the whole substrate surface, which is stable in time at room temperature. Although the interface of Pt with Bi2Se3 was found to be i less reactive compared to Ag and Ti, an interfacial phase formed upon annealing to ∼90 °C was detected by TEM cross section experiment. A model for prediction of interfacial reactions between a metal and Bi2Se3 based on the standard reduction potential of the metals and Gibbs free energy for a model reaction is presented. Based on these two values the reaction can be expected to result in the formation of binary and/or ternary selenides and Bi. Presented work shows on the importance of metal/topological insulator interfaces characterization taking into account the possibility of a chemical reaction with all of its consequences. Results should be considered for future theoretical and applicative studies involving such interfaces as well as for the possible engineering of 2D TI heterostructures.
Ključne besede: topological insulators, topological surface states, Bi2Se3, thin films, Ag, Ti, Pt, morphology, interfaces, solid-state reaction, metal selenides, reactivity, stability, electron microscopy, dissertations
Objavljeno v RUNG: 09.06.2021; Ogledov: 3867; Prenosov: 173
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13.
Sn-modified TiO[sub]2 thin film photocatalysts prepared by low-temperature sol-gel processing : dissertation
Ksenija Maver, 2021, doktorska disertacija

Opis: Due to many advantageous physiochemical properties, titanium dioxide (TiO2) is the most widely used photocatalyst in numerous applications, such as wastewater treatment and air purification, self-cleaning surfaces and energy conversion (H2 generation). However, one of its disadvantages is the high electron-hole recombination rate, and coupling with other semiconductors is one of the strategies to improve it. The objective of this dissertation was to investigate how the photocatalytic activity of pure TiO2 can be improved by tin modification and to explain the mechanism of increased or hindered photoactivity in correlation with the structural properties of the modified TiO2 photocatalysts. A new low-temperature sol-gel synthesis route was developed to prepare Sn- or SnO2-modified TiO2 photocatalysts. In both cases, organic tin and titanium precursors were used. Tin in the form of Sn cations was used to prepare Sn-modified TiO2. In this case, the precursors went through the sol-gel reaction together to form a Sn-TiO2 sol. In the case of SnO2 modification, the SnO2 sol was prepared separately and additionally mixed with the TiO2 sol to form a TiO2/SnO2 bicomponent semiconductor system. Different molar ratios of tin to titanium were prepared to investigate the correlation between the tin concentration and the photocatalytic properties of the photocatalysts in the form of thin films. The results were used to optimize the synthesis conditions to obtain an improved activity of the modified TiO2 photocatalysts under UV-irradiation. The photocatalytic activity of the thin films was determined by measuring the degradation rate of an azo dye. An increase of up to 40 % in the photocatalytic activity of the dried samples (at 150 °C) was achieved when the TiO2 was modified with the Sn or SnO2 in a concentration range of 0.1 to 1 mol.%. At higher Sn or SnO2 loadings and after calcination of the samples at 500 °C, the photocatalytic activity of the photocatalyst was reduced compared to the unmodified TiO2. Different characterization techniques (UV-Vis, XRD, nitrogen physisorption, TEM, SEM and XAS) were employed to clarify the mechanism responsible for the enhanced and hindered photocatalytic performance of the Sn- and SnO2-modified TiO2 photocatalysts. The results showed that a nanocrystalline structure is already achieved in the samples by the low-temperature film treatment (drying at 150 °C) and that the photocatalytic efficiency is mainly influenced by the crystalline phase composition: anatase/rutile in the case of Sn-modified and TiO2/SnO2 in the case of SnO2-modified TiO2. The crystal size and specific surface area differ insignificantly between the equally thermally treated samples and partly explain the differences in photoefficiency of the calcined samples compared to the dried samples. The structural study at the atomic level, using the Sn K-edge EXAFS, revealed that Sn cations act as nucleation sites for the anatase to rutile transformation in the Sn-modified TiO2 photocatalysts, while in the SnO2-modified TiO2 samples the nanocrystalline cassiterite SnO2 is bound to the TiO2 nanocrystallites via the Sn-O-Ti bond. In both cases, the advantage of coupling the two semiconductors was achieved by separating the charge carriers and thus prolonging their lifetime for accessibility to participate in the redox reactions. The maximum activity enhancement was achieved in the low concentration range (0.1–1 mol.%), which means that an optimal ratio and contact of the two phases are obtained for the given physical parameters, such as particle size, shape and specific surface area of the catalyst.
Ključne besede: Sn-modified TiO2, SnO2-modified TiO2, low-temperature sol-gel, thin films, photocatalytic activity, anatase/rutile system, Sn K-edge EXAFS, dissertations
Objavljeno v RUNG: 09.06.2021; Ogledov: 4640; Prenosov: 161
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14.
Photoelectrocatalytic water splitting and dye degradation with fluorine doped tin oxides films
Manel Machreki, Takwa Chouki, Saim Emin, 2019, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: We report the photoelectrochemical (PEC) water splitting with flourine doped tin oxide (FTO) films. This is the first study where efficient water splitting is achieved with FTO films under light illumination. Potentiostatic test at 1.7 V vs reversible hydrogen electrode (RHE) show that FTO material is very stable for water oxidation without occurence of a noticable current drop over a span of 6 hours. Mass spectrometry analysis of evolved gasses confermed the formation of oxygen and hydrogen in the two half cells (separated by a membrane). Moreover, it was demonstrated that the water splitting reaction involve formation of hydroxyl radicals (•OH) which are known oxidants for organics. We applied these FTO films for degradation of a model pollutant rhodamine B dye (1×10−5 mol/l). PEC assisted degradation of rhodamine B took about 30 min to achieve complete degradation of 60 ml model dye solution.
Ključne besede: FTO, thin films, dye degradation
Objavljeno v RUNG: 13.05.2021; Ogledov: 2147; Prenosov: 0
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15.
Electrocatalytic hydrogen evolution with textured iron phosphides thin films
Saim Emin, 2019, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: We used wet-chemistry techniques to prepare colloidal iron phosphides (F2P) nanoparticles (NPs). The synthesis of Fe2P NPs was conducted using the so called hot-matrix method [1]. The sizes of obtained Fe2P NPs are in the order of 2 - 5 nm. The colloidal Fe2P NPs are coated with hydrophobic molecules which allow preparation of stable dispersion in organic solvents like choloroform (CHCl3). The colloidal F2P NPs are very suitable for the preparation of thin films via spin-coated, spray coated or inkjet-printed on various conductive substrates. The obtained Fe2P films were used in hydrogen evolution reaction (HER). In addition, to HER the Fe2P films were used for electrocatalytic degradation of organics.
Ključne besede: Fe2P, electroctalysis, thin films
Objavljeno v RUNG: 13.05.2021; Ogledov: 2464; Prenosov: 0
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16.
Preparation of porous [alpha]-Fe[sub]2O[sub]3 thin films for efficient photoelectrocatalytic degradation of basic blue 41 dye
Manel Machreki, Takwa Chouki, Mitja Martelanc, Lorena Butinar, Branka Mozetič Vodopivec, Saim Emin, 2021, izvirni znanstveni članek

Opis: A novel method was developed for the preparation of porous hematite (α-Fe2O3) thin films. First, a solution containing iron precursor was spin-coated on fluorine-doped tin oxide substrate and later short heat-treated at 750 °C. The prepared α-Fe2O3 thin films were applied as dual-function catalyst in photoelectrochemical (PEC) water oxidation and textile dye degradation studies. For the first time, α-Fe2O3 thin films were used in efficient PEC degradation of a textile dye (Basic Blue 41 – B41) using in-situ generated reactive chlorine species. In comparison with photocatalytic and electrocatalytic approaches, the PEC technique allows faster degradation of B41 dye at an applied bias potential of 1.5 V versus reversible hydrogen electrode and under visible light illumination. In the presence of Cl− using the PEC approach the degradation of B41 reaches 99.8%. High-performance liquid chromatography coupled with UV–VIS system confirmed the degradation of B41 dye using PEC. Gas-chromatography coupled to mass spectrometry was used to study the by-products obtained during PEC degradation. Chemical oxygen demand analyses confirmed that the mineralization level of B41 is in the order of 68%. The α-Fe2O3 films developed in this study give a higher level of PEC degradation efficiency compared to other iron oxide-based systems.
Ključne besede: thin films, photoelectrocatalysis, kinetics, visible light, degradation, textile dye
Objavljeno v RUNG: 10.05.2021; Ogledov: 2436; Prenosov: 12
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17.
Chemical Instability of an Interface between Silver and Bi2Se3 Topological Insulator at Room Temperature
Katja Ferfolja, Matjaž Valant, Iuliia Mikulska, Sandra Gardonio, Mattia Fanetti, 2018, izvirni znanstveni članek

Opis: Understanding an interaction at an interface between a topological insulator and a metal is of critical importance when designing electronic and spintronic devices or when such systems are used in catalysis. In this paper, we report on a chemical instability of the interface between Bi2Se3 and Ag studied by X-ray powder diffraction and electron microscopy. We present strong experimental evidence of a redox solid-state reaction occurring at the interface with kinetics that is significant already at room temperature. The reaction yields Ag2Se, AgBiSe2, and Bi. The unexpected room-temperature chemical instability of the interface should be considered for all future theoretical and applicative studies involving the interface between Bi2Se3 and Ag.
Ključne besede: topological insulators, Ag, thin metal films, interfaces, redox reaction
Objavljeno v RUNG: 17.06.2020; Ogledov: 2971; Prenosov: 0
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18.
STUDY OF ELECTRONIC STATES OF THIN METAL FILMS ON HEAVY METAL SURFACES : MASTER'S THESIS
Luka Novinec, 2018, magistrsko delo

Opis: V magistrskem delu smo se osredoto£ili na pripravo in karakterizacijo heterogenih ve£plastnih tankih filmov sestavljenih iz kovin ter teºkih kovin. Za izdelavo vzorcev smo izbrali dve feromagnetni kovini, Fe in Gd, ter eno divalentno kovino iz redkih zemelj, Yb. Tanke filme smo nana²ali na kristalno povr²ino volframa W(110) ter molibdena Mo(110). V primeru Fe na povr²ini W(110) in Mo(110) ter Yb na pov²ini Mo(110) smo uspe²no dolo£ili pogoje, potrebne za nana²anje atomsko enakomernih filmov. S pomo £jo kotno odvisne fotoemisije smo preu£evali kvantna stanja v Fe in Yb filmih na Mo in W kristalih. Celotno eksperimentalno delo je potekalo na ºarkovnih linijah VUV-Photoemission in²tituta (ISM-CNR) ter BaDElPh pri sinhrotronu Elettra v Trstu.
Ključne besede: electronic states, thin metal films, heavy metal surfaces
Objavljeno v RUNG: 04.12.2019; Ogledov: 4088; Prenosov: 105
.pdf Celotno besedilo (25,10 MB)

19.
Photoactive nanocomposite thin films on glass and thermosensitive substrates
Nives Vodišek, 2019, doktorska disertacija

Opis: Photocatalysis is a well-known process for the last few decades; it is predominantly used for water and air purification, but also for self-cleaning and antibacterial surfaces. The photocatalytic process is one of the advanced oxidation processes, where semiconductors are mainly used as photocatalysts. The most known and used semiconductor is nanosized titania, which can non-selectively decompose organic matters. One of the side effects of nano TiO2 under UV irradiation is photoinduced hydrophilicity, which furthermore improves the self-cleaning effect. The main drawback of TiO2 is that for its activation UV light is needed, which represents only 5 percent of the solar spectrum. Consequently, actinic irradiance power is low and the response of photocatalyst is limited. Novel approaches are being introduced to improve TiO2 response to visible light such as doping, coupling, modification of surface morphology and others. The thesis consists of five principal chapters. The first chapter is focused on a short literature review and explanation of some basic terms and principles that are related to this thesis. The aim of the research was to prepare transparent photocatalytically active thin films on glass and thermosensitive substrates. Four thermosensitive substrates were used: polyvinyl chloride (PVC) foil, polymethyl methacrylate (PMMA) sheet and polyester (PES) fabric coated with a polyvinyl and acrylic coating, with (D1) or without (D2) an additional polyvinylidene fluoride topcoat. The synthesis of films was modified with the introduction of zirconium aiming at improving the photocatalytic activity of the TiO2 films, and the final films had a SiO2 phase present for increased mechanical robustness. The third chapter is dedicated to the experimental part of the thesis. The detailed process of synthesis is described. The sol-gel process was used to prepare initial Ti-Zr sols, colloidal aqueous solutions with TiO2 and ZrO2 nanoparticles derived from titanium and zirconium alkoxides. The four different Ti-Zr sols were prepared with 0, 5, 10 and 20 molar % of Zr according to Ti. The depositing solution was prepared by mixing Ti-Zr sol, SiO2 sol binder, 1-propanol and 2-propoxyethanol, and then thin films were deposited by dip-coating technique. After the deposition, samples did not require high-temperature calcination since the photocatalytic anatase phase was present already after drying the deposited layers. Coated glass slides were put into a furnace at 150 °C, while samples on thermosensitive substrates were just treated by a heat gun. Samples in powder and thin film form were characterized by UV-Vis, FTIR-ATR and laser beam deflection spectroscopy, X-ray diffraction, scanning electron microscopy and thermal analysis. One of the main aspects of the photocatalyst is its activity. Photocatalytic activity of the thin films was determined, either quantitatively by the formation of fluorescent hydroxyterephthalic acid, one of the first degradation products of terephthalic acid deposit, or qualitatively by a visual-based method where degradation of resazurin ink was observed. Two additional methods were used on glass samples, electron paramagnetic resonance, and degradation of methyl stearate by observing the change in water contact angle under UVA irradiation. Mechanical stability of films on various substrates is an essential factor, describing how successful was immobilization of the photocatalytic materials on the substrate. It was determined by the pencil hardness test, i.e., Wolff-Wilborn method. In the fourth chapter, titled “Results and Discussion,” the most important part of the thesis is placed. Materials characterization and associated discussion of the results are divided into three major parts: i) powder samples characterization; ii) characterization of thin films on a glass substrate, and iii) characterization of films on thermosensitive substrates. In the conclusions, the main findings of the Ph.D. research work are summarized. One of our initial hypotheses was disapproved, thin films were not more active with a higher content of zirconium. However, they were more durable. All the obtained films were transparent and photoactive, despite the low-temperature synthesis procedure. Besides commonly used glass substrate, immobilization on thermosensitive substrates was also successful.
Ključne besede: glass substrate, immobilization, nanocomposite, nanomaterials, PES, photocatalysis, PMMA, PVC, self-cleaning surfaces, silica, plastic substrates, thin films, titania, zirconia
Objavljeno v RUNG: 14.10.2019; Ogledov: 4027; Prenosov: 184
.pdf Celotno besedilo (6,23 MB)

20.
Determination of Fe(III) and Fe(II) in natural waters using passive DGT samplers and non-destructive BDS analysis
Hanna Budasheva, Dorota Korte, Arne Bratkič, Mladen Franko, 2019, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: Beam Deflection Spectrometry, iron species, Diffusive Gradients in Thin-films, frequency scanning
Objavljeno v RUNG: 30.09.2019; Ogledov: 3397; Prenosov: 0
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