141. Tungsten carbide thin films for electrochemical water splitting studiesSaim Emin, Cesur Altinkaya, Ali Semerci, Matjaž Valant, Hasan Okuyucu, Abdullah Yildiz, 2017, objavljeni povzetek znanstvenega prispevka na konferenci Opis: We used wet-chemistry techniques to prepare colloidal tungsten (W) nanoparticles (NPs). The synthesis of W NPs was conducted using the so called hot-matrix method in 1-octadecene [1]. The sizes of obtained W NPs are in the order of 2 - 5 nm. These W NPs are coated with hydrophobic molecules which allow their dispersion in organic solvents like choloroform (CHCl3). It was found that the colloidal stability of the dispersions is exceptionally high exceeding several years. The stability of W NPs which prevents coagulation allows the preparation of thin films with uniform thicknesses by spin-coating, inkjet-printing and spray coating.
We have prepared tungsten carbide (W2C, WC) thin films. The preparation of W2C and WC was achieved by spin-coating of pre-synthesized W NPs on graphite substrate and following heat treatment under Ar atmosphere at 1000 and 1450°C.
The obtained W2C and WC films were used both in electrochemical water splitting studies. We also made a composite W2C-Pt films where we used only 5 at.% of Pt. The W2C-Pt composite has shown similar performance as pure Pt-C for hydrogen (H2) evolution. In conclusion, we have developed a procedure for the synthesis of W NPs which can be applied for the preparation of tungsten carbides films and their use for electrochemical water splitting.
Ključne besede: water splitting, nanoparticles, hot-matrix
Objavljeno v RUNG: 09.10.2017; Ogledov: 5993; Prenosov: 0
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142. FROM SPINODAL DECOMPOSITION AND MOLECULAR DISPERSION OF POLYSILANES TO SUPER-HARD NANOCOATINGArtem Badasyan, Boštjan Mavrič, Matjaž Valant, objavljeni povzetek znanstvenega prispevka na konferenci Opis: Conformations of polymer molecules in solution crucially depend on the sign of the
effective potential energy of interaction between the monomers, also known as the
quality of solvent. Therefore in “poor” solvent regime, when effective attraction
overwhelms, the experimental measurements of polymer sizes are complicated by the
agglomeration of macromolecules, followed by precipitation. This phenomenon, also
known as spinodal decomposition, causes serious problems when the goal is to
determine properties of individual macromolecules. Interestingly, while in the case of
carbon-based polymers the precipitation-related problems can be easily avoided with
dilution, this is not the case for polysilanes, i.e. polymeric chains on basis of silicon.
Although the linear polysilanes were first synthesized in early 1920’s, the aggregationrelated
problems have hampered their studies and applicability until recently.
In the Materials Research Laboratory of University of Nova Gorica we have developed
a technology to strengthen the scratch-resistance nanocoating for glass on the basis of
polysilane dendritic polymers we synthesized. Through the prism of the Flory-Huggins
theory, that provides a miscibility phase diagram in temperature-volume fraction
variables, the quality of polymer solution can be manipulated by changing the
temperature. Using Dynamic Light Scattering (DLS) and Differential Scanning
Calorimetry (DSC) we have managed to show, that at temperatures in the range of 40-
50 C the deagglomeration of the dendritic polysilane takes place in tetrahydrofuran
(THF) [1], and the system becomes a true molecular dispersion with particles 20 nm in
size [2]. Introducing such molecular dispersion into the alumina precursor solution
yields an amorphous nanocomposite stabilized by a high level of strain. This resulted in
an extraordinary increase of hardness and scratch resistance of the alumina – polymer
nanocomposite coating that can be used for glass protection [3].
Ključne besede: Polysilane, dendrimer, solubility
Objavljeno v RUNG: 12.09.2017; Ogledov: 4360; Prenosov: 0
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145. Design of a highly photocatalytically active ZnO/CuWO4 nanocompositeSaim Emin, Matjaž Valant, 2017, objavljeni povzetek znanstvenega prispevka na konferenci (vabljeno predavanje) Opis: We report the synthesis, photocatalytic activity and mechanistic study of a novel heterostructure (HTS) with an efficient charge separation. A ZnO/CuWO4 HTS material is reported for the first time. The nanocomposite (NC) consists of CuWO4 nanoparticles (ca. 200-400 nm) decorated with ZnO nanorods (ca. 30 nm, 100 nm length) and is shown to be a highly active photocatalyst for decomposition of model contaminants including methyl orange and terephthalic acid. The ZnO/CuWO4 interface is shown to be the key for controlling the enhanced activity of the composite material. Transient absorption spectroscopy studies demonstrated that a photoinduced charge transfer across the ZnO/CuWO4 interface increased electron-hole lifetime by 3 orders of magnitude, from < 20 s in ZnO to 30 ms in the ZnO/CuWO4 NC sample. Our findings show that through interface design efficient HTS materials can be prepared for a wide range of photocatalytic applications.
Ključne besede: CuWO4, nanocomposite, transient absorption spectroscopy
Objavljeno v RUNG: 28.08.2017; Ogledov: 5088; Prenosov: 0
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146. Atomic-level mechanisms of magnesium oxidationSandra Gardonio, Mattia Fanetti, Matjaž Valant, Dmytro Orlov, 2016, objavljeni znanstveni prispevek na konferenci Opis: Magnesium has been recently becoming an increasingly popular material for various applications. However, excessive chemical reactivity, and oxidation rate in particular, is a major obstruction on the way of Mg to become widely adopted. A significant problem causing the lack of Mg reactivity control is insufficient understanding of mechanisms involved in the oxidation of magnesium surface. Herewith we present the investigation of atomic-level mechanisms of oxidation initiation and propagation in pure Mg. Namely, X-ray photoelectron spectroscopy at synchrotron Elettra was used as a surface sensitive direct method to determine the valence of Mg and O and the valence band states at the early stage of oxide formation over a principal, most densely packed, crystallographic plane (0001) in pure Mg. The mechanisms of oxygen adsorption on magnesium free surface followed by oxidation (i.e. initiation and kinetics of MgO formation) are clarified. Copyright © 2016 by The Minerals, Metals & Materials Society. All rights reserved.
Ključne besede: Magnesium, Oxidation, Synchrotron radiation, X-ray photoelectron spectroscopy
Objavljeno v RUNG: 25.08.2017; Ogledov: 5069; Prenosov: 0
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