41. Tungsten carbide thin films for electrochemical water splitting studiesSaim Emin, Cesur Altinkaya, Ali Semerci, Matjaž Valant, Hasan Okuyucu, Abdullah Yildiz, 2017, published scientific conference contribution abstract Abstract: 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.
Keywords: water splitting, nanoparticles, hot-matrix
Published in RUNG: 09.10.2017; Views: 5990; Downloads: 0
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42. Design of a highly photocatalytically active ZnO/CuWO4 nanocompositeSaim Emin, Matjaž Valant, 2017, published scientific conference contribution abstract (invited lecture) Abstract: 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.
Keywords: CuWO4, nanocomposite, transient absorption spectroscopy
Published in RUNG: 28.08.2017; Views: 5088; Downloads: 0
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43. Involving CeVO4 in improving the photocatalytic activity of a Bi2WO6/allophane composite for the degradation of gaseous acetaldehyde under visible light Mirabbos Hojamberdiev, Zuhra Kadirova, Yuki Makinose, Gangqiang Zhu, Saim Emin, Nobuhiro Matsushita, Masashi Hasegawa, Kiyoshi Okada, 2017, original scientific article Abstract: Indoor air quality is affected by hazardous chemical substances emitted from buildings, construction and decoration materials, indoor equipments or even due to human activities. In this study, the hydrothermal synthesis and mechanical mixing were applied to synthesize Bi2WO6/CeVO4/allophane composites (BW/CV/A), and their photocatalytic performance for the degradation of acetaldehyde, as a common indoor air pollutant, was evaluated under visible-light irradiation. The as-prepared composites were characterized by X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and UV–visible (UV–vis) spectroscopy. The results demonstrated that the prepared composites had microstructures consisting of nanosheets of hierarchical flower-like Bi2WO6 microspheres on which the CeVO4 nanocrystals were fully embedded in the presence of allophane nanoparticles. The specific surface areas of the as-synthesized and mechanically mixed BW1/CV1/A composites were in the range of 110–182 m2 g−1. The effect of the amount of CeVO4 on photocatalytic activity of the Bi2WO6/allophane composite was explored, and the highest photocatalytic activity was observed for the BW1/CV1/A composite (Bi2WO6:CeVO4 = 1:1 mass ratio). Compared with the Bi2WO6/allophane and CeVO4/allophane composites, the hydrothermally synthesized BW1/CV1/A composite showed a significantly higher photocatalytic activity for the degradation of acetaldehyde under visible-light irradiation. The enhancement in the photocatalytic activity of the Bi2WO6/allophane composite achieved by involving the CeVO4 nanocrystals is due presumably to an extended light absorption range, appropriate band structures of Bi2WO6 and CeVO4, the formed p–n heterojunction, and the co-existence of Ce3+ and Ce4+ in CeVO4, resulting in effective separation of photogenerated electron-hole pairs.
Published in RUNG: 16.08.2017; Views: 4569; Downloads: 0
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44. Synthesis and characterization of metal/semiconductor nanocomposites for photocatalysisTina Mavrič, doctoral dissertation Abstract: The doctoral dissertation focused on improving photocatalytic activity of nanopowdered ZnO by constructing I) Metal-Semiconductor and II) Semiconductor-Semiconductor heterostructures. Both heterostructure types have been reported to have a beneficial effect on photocatalytic efficiency. For the first part (I) Ag/ZnO nanocomposite was synthesized. Here we investigated an influence of polyvinylpyrrolidone (PVP) addition during the synthesis on the particle properties and their photoactivity. The second part (II) describes procedure development of ZnO based semiconductor-semiconductor composite that resulted in synthesis of highly efficient ZnO/CuWO4 composite.
Ag/ZnO nanocomposite was synthesized from precursors in ethylene glycol (EG) in a hydrothermal reactor at 180 °C for 3h. No further thermal treatment was required after the synthesis since all samples showed good crystallinity. Silver precursor loading was 2.7 wt%, because this amount has shown the best photoactivity in preliminary sample testings. Two separate batches of Ag/ZnO nanopowders were prepared, one with addition of PVP, one without (labelled Ag/ZnO and Ag/ZnO*, respectively). All powders were in nanometer range, TEM images showed a major difference between the samples with and without PVP. While Ag nanoparticles were deposited uniformly over ZnO, Ag/ZnO* exhibited a substantial agglomeration of Ag. The photocatalytic efficiency was assessed under UV-Vis light. Ag/ZnO reached complete decolourization of 10–5 M methyl orange (MO) already in 80 min after the beginning of irradiation. The calculated degradation rate constant (k) for the Ag/ZnO was almost 2-times larger than for TiO2 P25 and 4-times larger than for ZnO. Ag/ZnO* also showed higher activity than pure ZnO*, but was inferior to Ag/ZnO (1.6-times of Ag/ZnO*). A reusability test performed on Ag/ZnO showed an excellent photoactivity of reused powders; second and third cycle exhibited higher photoactivity than the first cycle. The supreme photocatalytic activity of Ag/ZnO was also confirmed by degradation of terephthalic acid.
To develop an efficient semiconductor-semiconductor heterostructure we have synthesized a combination of several materials with ZnO. We performed preliminary photocatalytic tests in order to assess the functionality of these heterostructures. The tested systems were the following: ZnO/MWCNT, ZnO/GO, ZnO/SiC, ZnO/Co3O4, ZnO/AgVO3. The synthesis of heterostructures was done via hydrothermal synthesis. The commercial or synthesized powers were dispersed together with the ZnO precursor in EG medium (180 °C/3h). The aim was to obtain higher photoactivity than that of pure ZnO. None of these systems was able to outperform pure ZnO.
ZnO/CuWO4 system has, however, significantly improved ZnO photoactivity. Several synthesis routes were investigated, including the influence of different structure directing agents (PVP, CTAB, starch). The best performing system was obtained by separate hydrothermal synthesis of ZnO and CuWO4 in water with PVP. XRD analysis confirmed that to obtain the crystalline CuWO4 thermal treatment (500 °C) is needed. The heterostructure was also synthesized in ethanolic solution. ZnO particles were in a nanometer range, CuWO4 were larger and ranged from 200 to 400 nm. CuWO4 has successfully decreased the charge recombination in ZnO, which was confirmed by transient absorption spectroscopy studies. The photocatalytic activity was assessed for both MO and TPA (10–4 M) degradation. The ZnO/CuWO4 composite has completely decolourized the dye in 60 min of UV-Vis irradiation. k for ZnO/CuWO4 was ~2.5-times larger than that of ZnO. A 3-cycle reusability test with MO showed a small decrease in efficiency in the last cycle. TPA degradation has revealed lower efficiency for ZnO/CuWO4 in air but high efficiency in O2 and N2 atmosphere, where it reached 90% and 55% degradation rate, respectively.
Keywords: photocatalysis, zinc oxide, heterostructures, powders, Ag/ZnO composites, ZnO/CuWO4 composites
Published in RUNG: 31.05.2017; Views: 6248; Downloads: 362
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45. Interface-controlled growth of organic semiconductors on grapheneJinta Mathews, Saim Emin, Egon Pavlica, Matjaž Valant, Gvido Bratina, 2017, original scientific article Abstract: We have studied submonolayer coverages of N,N-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDIF-CN2) on mechanically exfoliated graphene transferred onto SiO2 substrates. Our atomic force microscopy (AFM) data show that PDIF-CN2 forms irregularly-shaped 1.4 nm-high islands. From the selected area diffraction performed with transmission electron microscope (TEM) we conclude that this height corresponds to π−π
stacks of molecules, which are inclined for 43° relative to the graphene surface. AFM also showed complete absence of PDIF-CN2 on single-layer graphene (SLG). Electric force microscopy revealed a marked difference in surface charge density between a single-layer graphene and bilayer graphene, with a higher surface charge on SLG than on the bilayer graphene. We associate this behavior with p−
type doping of graphene due to the electrostatic dipole induced by the molecular water layer present at the graphene/SiO2 interface. The crucial role of the graphene/SiO2 interface in determining growth of PDIF-CN2 was further confirmed by TEM examination of PDIF-CN2 deposited onto unsupported SLG.
Keywords: afm, organic semiconductors, graphene
Published in RUNG: 18.05.2017; Views: 4827; Downloads: 0
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46. Electron Microscopic Visualization of Complementary Labeled DNA With Platinum-Containing Guanine DerivativeAlexandre Loukanov, Chavdar Filipov, Polina Mladenova, Svetlin TOSHEV, Saim Emin, 2016, original scientific article Abstract: The object of the present report is to provide a method for a visualization of DNA in TEM by complementary labeling of cytosine with guanine derivative, which contains platinum as contrast-enhanced heavy element. The stretched single-chain DNA was obtained by modifying double-stranded DNA. The labeling method comprises the following steps: (i) stretching and adsorption of DNA on the support film of an electron microscope grid (the hydrophobic carbon film holding negative charged DNA); (ii) complementary labeling of the cytosine bases from the stretched single-stranded DNA pieces on the support film with platinum containing guanine derivative to form base-specific hydrogen bond; and (iii) producing a magnified image of the base-specific labeled DNA. Stretched single-stranded DNA on a support film is obtained by a rapid elongation of DNA pieces on the surface between air and aqueous buffer solution. The attached platinum-containing guanine derivative serves as a high-dense marker and it can be discriminated from the surrounding background of support carbon film and visualized by use of conventional TEM observation at 100 kV accelerated voltage. This method allows examination of specific nucleic macromolecules through atom-by-atom analysis and it is promising way toward future DNA-sequencing or molecular diagnostics of nucleic acids by electron microscopic observation.
Keywords: DNA stretching and visualization, contrast-enhanced Pt-containing guanine, DNA sequences
Published in RUNG: 02.02.2017; Views: 4846; Downloads: 0
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47. Biotinylated Vanadium and Chromium Sulfide Nanoparticles as Probes for Colocalization of Membrane ProteinsAlexandre Loukanov, Saim Emin, 2016, original scientific article Abstract: ABSTRACT We report the microemulsion synthesis of vanadium and chromium sulfide nanoparticles (NPs) and their biological application as nanoprobes for colocalization of membrane proteins. Spherical V2S3 and Cr2S3 NPs were prepared in reverse microemulsion droplets, as nanoreactors, obtained by the surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in nonpolar organic phase (heptane). Electron microscopic data indicated that the size distribution of the nanoparticles was uniform with an average diameter between 3 4 5 nm. The prepared hydrophobic nanocrystals were transferred in aqueous phase by surface cap exchange of AOT with biotindihydrolipoic ligands. This substitution allows the nanoparticles solubility in aqueous solutions and confer their bioactivity. In addition, we report the conjugation procedure between a-Lipoic acid (LA) and biotin (abbreviated as biotin-LA). The biotin-LA structure was characterized by 1D and 2D NMR spectroscopy. The biotinylated vanadium and chromium sulfide nanoparticles were tested as probes for colocalization of glutamate receptors on sodium-dodecyl-sulfate-digested replica prepared from rat hippocampus. The method suggests their high labeling efficiency for study of membrane biological macromolecules.
Keywords: biotin-dihydrolipoic conjugate, vanadium and chromium sulfide nanoparticles, membrane proteins
Published in RUNG: 02.02.2017; Views: 5293; Downloads: 0
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49. Bakrov klorid – 1 μmNarvika Bovcon, Aleš Vaupotič, 2014, artistic work Abstract: Narvika Bovcon, Aleš Vaupotič, v sodelovanju z: Saim Emin (priprava vzorcev), Mattia Fanetti (operater vrstičnega elektronskega mikroskopa). Digitalna grafika, steklo, okvir, dimenzije: 65 × 56 cm (ležeče), črno-belo. 2014. Produkcija: Univerza v Novi Gorici, projekt SUNGREEN.
Keywords: tehniška slika, novomedijska umetnost, materiali, mikroskopija, vrstični elektronski mikroskop, SEM
Published in RUNG: 12.05.2016; Views: 4678; Downloads: 24
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50. Bakrov klorid – 10 nmNarvika Bovcon, Aleš Vaupotič, 2014, artistic work Abstract: Narvika Bovcon, Aleš Vaupotič, v sodelovanju z: Saim Emin (priprava vzorcev), Mattia Fanetti (operater vrstičnega elektronskega mikroskopa). Digitalna grafika, steklo, okvir, dimenzije: 65 × 56 cm (ležeče), črno-belo. 2014. Produkcija: Univerza v Novi Gorici, projekt SUNGREEN.
Keywords: tehniška slika, novomedijska umetnost, materiali, mikroskopija, vrstični elektronski mikroskop, SEM
Published in RUNG: 12.05.2016; Views: 5069; Downloads: 20
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