71. Synthesis and characterization of metal/semiconductor nanocomposites for photocatalysisTina Mavrič, doktorska disertacija Opis: 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.
Ključne besede: photocatalysis, zinc oxide, heterostructures, powders, Ag/ZnO composites, ZnO/CuWO4 composites
Objavljeno v RUNG: 31.05.2017; Ogledov: 6249; Prenosov: 362
 Celotno besedilo (4,11 MB) |
72. |
73. |
74. Biotinylated Vanadium and Chromium Sulfide Nanoparticles as Probes for Colocalization of Membrane ProteinsAlexandre Loukanov, Saim Emin, 2016, izvirni znanstveni članek Opis: 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.
Ključne besede: biotin-dihydrolipoic conjugate, vanadium and chromium sulfide nanoparticles, membrane proteins
Objavljeno v RUNG: 02.02.2017; Ogledov: 5294; Prenosov: 0
Gradivo ima več datotek! Več... |
75. One-pot synthesis of biocompatible silver nanoparticle composites from cellulose and keratin: characterization and antimicrobial activityChieu Ding Tran, Franja Prosenc, Mladen Franko, Gerald Benzi, 2016, izvirni znanstveni članek Opis: A novel, simple method was developed to synthesize biocompatible composites containing 50% cellulose (CEL) and 50% keratin (KER) and silver in the form of either ionic (Ag+) or Ag0 nanoparticle (Ag+NPs or Ag0NPs). In this method, butylmethylimmidazolium chloride ([BMIm+Cl-]), a simple ionic liquid, was used as the sole solvent and silver chloride was added to the [BMIm+Cl-] solution of [CEL+KER] during the dissolution process. The silver in the composites can be maintained as ionic silver (Ag+) or completely converted to metallic silver (Ag0) by reducing it with NaBH4. Results of spectroscopy (Fourier-transform infrared (FTIR), X-ray diffraction (XRD)) and imaging (scanning electron microscope (SEM)) measurements confirm that CEL and KER remain chemically intact and homogeneously distributed in the composites. Powder X-ray diffraction (XRD) and SEM results show that the silver in the [CEL+KER+Ag+] and [CEL+KER+Ag0] composites is homogeneously distributed throughout the composites in either Ag+ (in the form of Ag2O nanoparticles (NPs)) or Ag0NPs form with size of (9 ± 1) nm or (27 ± 2) nm, respectively. Both composites were found to exhibit excellent antibacterial activity against many bacteria including Escherichia coli, Staphylococus aureus, Pseudomonas aeruginosa, methicillin resistant Staphylococus aureus (MRSA), vancomycin resistant Enterococus faecalis (VRE). The antibacterial activity of both composites increases with the Ag+ or Ag0 content in the composites. More importantly, for the same bacteria and the same silver content, [CEL+KER+Ag0] composite exhibits relatively greater antimicrobial activity against bacteria compared to the corresponding [CEL+KER+Ag+] composite. Experimental results confirm that there was hardly any Ag0NPs release from the [CEL+KER+Ag0NPs] composite, and hence its antimicrobial activity and biocompatibility is due, not to any released Ag0NPs but rather entirely to the Ag0NPs embedded in the composite. Both Ag2ONPs or Ag0NPs were found to be toxic to human fibroblasts at higher concentration (>0.72 mmol), and that for the same silver content, [CEL+KER+Ag2ONPs] composite is relatively more toxic than [CEL+KER+Ag0NPs] composite. As expected, by lowering the Ag0NPs concentration to 0.48 mmol or less, the [CEL+KER+Ag0NPs] composite can be made biocompatible while still retaining its antimicrobial activity against bacteria such are E. coli, S. aureus, P. aeruginosa, MRSA, VRE. These results together with our previous finding that [CEL+KER] composites can be used for controlled delivery of drugs such as ciprofloxacin clearly indicate that the [CEL+KER+Ag0NPs] composite possess all required properties for successfully used as high performance dressing to treat chronic ulcerous infected wounds.
Ključne besede: Celulose, Keratin, Cmposites, Biocompatible, Ag nanoparticles, one-pot synthesis, Antibacterial, Antiviral
Objavljeno v RUNG: 28.11.2016; Ogledov: 5124; Prenosov: 0
Gradivo ima več datotek! Več... |
76. Packing patterns of silica nanoparticles on surfaces of armored polystyrene latex particlesSara Fortuna, Catheline A. L. Colard, Stefan A. F. Bon, Alessandro Troisi, 2009, izvirni znanstveni članek Opis: Fascinating packing patterns of identical spherical and discotic objects on curved surfaces occur readily in nature and science. Examples include C60 fullerenes,(1, 2)13-atom cuboctahedral metal clusters,(3) and S-layer proteins on outer cell membranes.(4) Numerous situations with surface-arranged objects of variable size also exist, such as the lenses on insect eyes, biomineralized shells on coccolithophorids,(5) and solid-stabilized emulsion droplets(6) and bubbles.(7) The influence of size variations on these packing patterns, however, is studied sparsely. Here we investigate the packing of nanosized silica particles on the surface of polystyrene latex particles fabricated by Pickering miniemulsion polymerization of submicrometer-sized armored monomer droplets. We are able to rationalize the experimental morphology and the nearest-neighbor distribution with the help of Monte Carlo simulations. We show that broadening of the nanoparticle size distribution has pronounced effects on the self-assembled equilibrium packing structures, with original 12-point dislocations or grain-boundary scars gradually fading out.
Ključne besede: packing patterns, silica, simulation, Monte Carlo, order, disorder, transition, armored particles, nanoparticles, Pickering emulsion
Objavljeno v RUNG: 10.10.2016; Ogledov: 4674; Prenosov: 0
Gradivo ima več datotek! Več... |
77. |
78. Search for Ultra-relativistic Magnetic Monopoles with the Pierre Auger ObservatoryToshihiro Fujii, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Darko Veberič, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2015, objavljeni znanstveni prispevek na konferenci Opis: Ultra-relativistic magnetic monopoles, possibly a relic of
phase transitions in the early universe, would deposit an
amount of energy comparable to UHECRs in their passage
through the atmosphere, producing highly distinctive air
shower profiles. We have performed a search for
ultra-relativistic magnetic monopoles in the sample of air
showers with profiles measured by the fluorescence detector of
the Pierre Auger Observatory. No candidate was found to satisfy
our selection criteria and we establish upper limits on the
flux of ultra-relativistic magnetic monopoles - the first from
an UHECR detector - improving over previous results by up to an
order of magnitude.
Ključne besede: ultra-relativistic magnetic monopoles, extensive air showers, Pierre Auger Observatory
Objavljeno v RUNG: 03.03.2016; Ogledov: 4629; Prenosov: 195
Celotno besedilo (188,24 KB) |
79. Search for energy dependent patterns in the arrival direction of cosmic rays at the Pierre Auger ObservatoryTobias Winchen, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Darko Veberič, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2015, objavljeni znanstveni prispevek na konferenci Opis: Energy-dependent patterns in the arrival directions of cosmic
rays are expected from deflections in galactic and extragalactic magnetic fields. We report on searches for such
patterns in the data of the surface detector of the Pierre
Auger Observatory at energies above E = 5 EeV in regions
within approximately 15◦ around events with energy E > 60
EeV. No significant patterns are found with this analysis which
can be used to constrain parameters in propagation scenarios.
Ključne besede: ultra-high energy cosmic rays
galactic and extragalactic magnetic fields
magnetic deflection patterns
Pierre Auger Observatory
Objavljeno v RUNG: 02.03.2016; Ogledov: 5338; Prenosov: 228
Celotno besedilo (1019,52 KB) |
80. Development of Advanced TiO2/SiO2 Photocatalyst for Indoor Air CleaningAndraž Šuligoj, 2015, doktorska disertacija Opis: TiO2 - SiO2 composites were synthesized by low-temperature sol-gel impregnation method, using four different titania sources (P-25 from Degussa, PC500 from Millennium, CCA 100 AS and CCA 100 BS from Cinkarna, later denoted as AS and BS, respectively) and deposited on aluminium and glass carriers. Ordered and disordered mesoporous silicas were impregnated with ce{TiO2} in powder or suspension form in the Ti : Si molar ratio 1 : 1. Structure, size, band gap, chemical composition and specific surface area of nanoparticles were determined by X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DR-UV-vis), Fourier transform infrared spectroscopy (FT-IR) and ce{N2} physisorption. Additionally, quantity of surface hydroxyl groups, surface acidity and mechanical stability of the coatings were determined by temperature programmed Fourier transform infrared spectroscopy (TPD-IR) and Wolff-Wilborn method, respectively. The photocatalytic activity of TiO2 and TiO2 - SiO2 composites was evaluated in the photodegradation of toluene and formaldehyde, as model VOCs, under UVA light irradiation in lab-made photoreactor system with two different regimes; batch and plug-flow mode. These two VOCs are being considered as examples of two of the six major classes of indoor air contaminants.
Adsorption properties of the samples with toluene, have shown that the addition of mesoporous silica was beneficial. The increase of the adsorption of the bare AS TiO2 (9.5 %) was higher in the case of ordered silica, SBA-15 (2.8 times for AS/SBA15 to 26.8 %) than disordered SiO2 KIL-2 (2.4 times for AS/KIL2 to 22.7 %) although it was significant in both types of mesoporous silica supports (over 20 %). Adsorption was found to be dependent mostly on the quantity of surface Si-OH groups.
Regarding the photocatalytic activities towards toluene degradation, the results with pure TiO2 showed the fastest kinetics in case of sample AS followed by PC500 and P25. The observed behaviour was ascribed to smaller particle size, and consequently higher specific surface area. Grafting titania onto silica showed the importance of structural parameters. Most importantly, if the pore structure of bare TiO2 collapsed, this resulted in decreased activity. On the other hand, retainment of the pore structure improved the distribution of nanoparticles, crystallinity and optical properties, which resulted in improved photocatalytic activity.
In the degradation of formaldehyde, it was found that adsorption and degradation abilities of the materials were much more dependent on the structural properties of the samples, i.e., the pore structure. This was explained as a consequence of the different degradation mechanisms of both pollutants. Toluene degradation is governed by the oxidation through photogenerated holes - direct oxidation, whereas in the degradation of formaldehyde, the major oxidative species are OH radicals. In addition, the same as in toluene oxidation, the activity was dependent mainly on the number of crystal defects and the band gap values, that is the oxidation and reduction potentials of the catalysts. The degradation efficiency was increased from 88 % in pure AS TiO2 to 97 % when this titania was grafted onto colloidal silica (7C).
An important highlight of the thesis is synthesis of a novel photocatalyst, labelled AS7C, which comprises an acidic colloidal suspension AS as TiO2 source and colloidal silica, using a low-temperature sol-gel impregnation method. This sample used all the above mentioned properties that improve photocatalytic activity towards both pollutants. Mechanical stability of the samples was also tested. The tests showed that binder, in the form of colloidal SiO2 (in size of 25 nm) in combination with colloidal titania of appropriate size - 6 nm, produced the highest mechanical stability of the coatings, which also showed excellent photocatalytic activity. Stability of the coatings, using AS as titania source, was greatly improved. The Wolff-Wilborn test on AS coating showed no mechanical resistance, while with the optimal (in terms of photocatalytic performance) addition of 7C SiO2 binder stability was excellent (F, which is in the middle of 6B-6H hardness scale). This sample (AS7C) was also tested for release of aerosols, during operation of the reactor, which could be harmful for human health at longer exposure times. It was found that aerosols are formed, probably as a consequence of detachment of nanoparticles in the first period of photodegradation test. However, their formation in consecutive tests was greatly reduced. Last but not least, a pilot plug-flow reactor was constructed to test the photocatalyst's efficiency in one-pass degradation of toluene. Sample AS7C was able to degrade toluene at conditions applied (v= 400 mL/min, m(catalyst) = 1049 mg, C(0) = 1 ppmv), which means that the out-flow from reactor was clean of the pollutant and any possible intermediates, comprising only of humid air and CO2. Deactivation of the catalyst was found at higher air flow and higher initial concentration of the pollutant. However, the concentrations of pollutants in living conditions are few orders of magnitude lower, hence this is a promising result.
Ključne besede: Air remediation, TiO2 photocatalysis, Immobilization, Thin layers, TiO2/SiO2 composites
Objavljeno v RUNG: 31.08.2015; Ogledov: 8686; Prenosov: 201
Celotno besedilo (33,47 MB) |
