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1.
Design of a highly photocatalytically active ZnO/CuWO4 nanocomposite
Matjaž Valant, 2016, izvirni znanstveni članek

Najdeno v: ključnih besedah
Ključne besede: Photocatalysis Heterostructure Nanocomposite Methyl orange Terephthalic acid
Objavljeno: 08.09.2016; Ogledov: 1354; Prenosov: 0
.pdf Polno besedilo (1,63 MB)

2.
Design of a highly photocatalytically active ZnO/CuWO4 nanocomposite
Matjaz Valant, Saim Emin, 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.
Najdeno v: ključnih besedah
Ključne besede: CuWO4, nanocomposite, transient absorption spectroscopy
Objavljeno: 28.08.2017; Ogledov: 895; Prenosov: 0
.pdf Polno besedilo (621,87 KB)

3.
Amorphous nanocomposite of polycarbosilanes and aluminum oxide
Andraž Mavrič, 2018, doktorska disertacija

Opis: This work presents a paradigm for high temperature stabilization of bulk amorphous aluminium oxide. The thermodynamic stabilization is achieved by preparing a nanocomposite, where polymethylsilane dendritic molecules are dispersed in an aluminium hydroxide gel. Upon heat-treatment the gel transforms to the amorphous aluminium oxide that is stable up to 900°C. The dispersion of the macromolecules and their covalent bonding to the alumina matrix induce homogeneously distributed strain fields that keep the alumina amorphous. The first part of the thesis focuses on the synthesis, characterization and solubility properties of the dendritic polymethylsilane. The polymethylsilane is synthetized by electrochemical polymerization from trichloromethylsilane monomer. The polymerization mechanism, involving a single polymerization pathway, is identified. The polymer growth proceeds through reduction of the monomers to the silyl anions and their addition to the growing polymer. The solubility of three chemically related but topologically different polysilanes (linear, dendritic and network) were studied by dynamic light scattering. At room temperature the agglomerates in a range from 500 to 1300 nm are present. They undergo de-agglomeration at slightly elevated temperatures of around 40°C. The de-agglomeration results in formation of stable solutions, where a hydrodynamic diameter of the individual polymer molecules was measured to be in a range from 20 to 40 nm. The obtained diameters of two dendritic polymethylsilane macromolecules, synthesized under different electrolysis conditions, are much larger than the theoretical size estimated for an ideal dendrimer. We determined by 29Si NMR that the reason for this is in a large number of branching irregularities (defects) contained in the molecular structure. Combining the experimental values obtained by DLS and density measurements with a structural model that considers the branching irregularities, it is shown that the inclusion of the defects allows the dendritic polymer to exceed the sterical limitations and form the hyperbranched dendritic structure. The final size depends on a relative amount of the branching defects. In the second part, the synthetized polymethylsilane molecules were successfully used for the nanocomposite formation. The aluminium hydroxide gel with the dispersed polymethylsilane molecules was prepared as a precursor. Upon heat-treatment it gives the amorphous aluminium oxide stable up to 900°C. The dispersed macromolecules induce homogeneously distributed strain fields that keep the aluminium oxide amorphous during the thermal treatment the dispersed macromolecules covalently bind to the matrix, inducing the interface strain. The amorphous state was confirmed by the presence of penta-coordinated aluminium detected by 27Al NMR and a low bandgap measured by UV-vis absorption spectroscopy.
Najdeno v: ključnih besedah
Ključne besede: amorphous aluminium oxide, polymethylsilane, nanocomposite, electropolymerization, solubility, agglomeration, de-agglomeration, dendrimer, hyperbranched dendritic structure, dynamic light scattering, thermal analysis, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, infrared spectroscopy, UV-Vis spectroscopy
Objavljeno: 19.07.2018; Ogledov: 921; Prenosov: 50
.pdf Polno besedilo (5,07 MB)

4.
High-temperature stabilization of bulk amorphous Al2O3
Andraž Mavrič, Matjaž Valant, Gregor Mali, Mattia Fanetti, 2018, izvirni znanstveni članek

Opis: We present a method for high temperature stabilization of bulk amorphous aluminium oxide. The stabilization is achieved by dispersing polysilane dendritic molecules in aluminium hydroxide gel, which upon thermal treatment gives amorphous aluminium oxide stable up to 900 °C. The dispersed macromolecules covalently bind to the alumina matrix and induce homogeneously distributed strain fields that keep the alumina amorphous. The thermal conversion of the precursor system was followed by thermogravimetry with an evolved gas analysis, infrared spectroscopy and 29Si NMR. The amorphous structure of aluminium oxide was confirmed with an X-ray and electron diffraction. Additionally, the amorphous state was supported by presence of penta-coordinated aluminium detected by 27Al NMR and a low bandgap measured by a UV–visible absorption spectroscopy.
Najdeno v: ključnih besedah
Povzetek najdenega: ...Amorphous aluminium oxide, Polysilane, Nanocomposite, Stabilization...
Ključne besede: Amorphous aluminium oxide, Polysilane, Nanocomposite, Stabilization
Objavljeno: 30.07.2018; Ogledov: 724; Prenosov: 0
.pdf Polno besedilo (2,67 MB)

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