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1.
Bi2O3-BASED PYROCHLORE NANOSTRUCTURES AND THEIR CRYSTALLOGRAPHIC, OPTOELECTRONIC AND PHOTOCATALYTIC PROPERTIES
Metka Benčina, 2015, doctoral dissertation

Abstract: Bi2O3-based pyrochlore nanomaterials and their photocatalytic, optoelectronic and crystallographic properties are the research topics of this doctoral dissertation. We synthesized these materials at nanoscale, since they are expected to possess photoactivity in the visible-light spectrum, which is an important target for the high-performance photocatalysts. To prepare nanoparticles that are not agglomerated, different synthesis methods (coprecipitation, coprecipitation followed by the digestion, reverse micelle) and post-treatments (furnace or hydrothermal reactor) were examined. Micrometer size materials were prepared with the solid-state reaction and annealing at high temperature. Bi2Ti2O7 nanoparticles were synthesized with the coprecipitation reaction, followed by annealing at 570 °C in the furnace or in the hydrothermal reactor at 230 °C for 18h in NH4OH medium. UV-Vis diffuse reflectance spectra of the Bi2Ti2O7 samples showed that they exhibit the maximum absorption edge at ~420-440 nm. The UV-Vis diffuse reflectance measurements of Bi2Ti2O7 loaded with 10 wt. % of Ag as a co-catalyst showed an enhanced absorbance in the visible region, presumably due to a contribution of Local Surface Plasmon Resonance. The Bi2Ti2O7 nanoparticles are not photocatalytically active under the visible light irradiation without assistance of a sacrificial reagent. The photocatalytic activity does not increase even with Ag as a co-catalyst under visible light irradiation. All samples are active under UV light irradiation, especially the sample with Ag that is able to decolourize 7 mg/L of metyl orange in just 3 min of exposure to UV light. However, H2O2 as a sacrificial reagent increases the photocatalytic activity of Bi2Ti2O7 under visible light irradiation. Phase pure pyrochlore Bi1.647Nb1.118Fe1.157O7 (BNF) nanoparticles were synthesized with coprecipitation reaction and further annealing in the furnace at 570 °C for 7h or 15h and in the hydrothermal reactor at 160 °C for 18h in 3 M or 6 M NaOH medium. The BNF materials exhibit shift toward longer wavelengths in absorbance of visible light (up to ~550-650 nm). This result confirmed that incorporation of Fe in the pyrochlore structure decreases the band gap. The BNF nanoparticles annealed for 7h showed intense photoactivity under visible light irradiation in the presence of a sacrificial reagent. The improved photoactivity, much better than with BNF, was shown for the composite nanoparticles BiOCl/BNF. They decolourize 100 % of the 7 mg/L methyl orange within only 2h of the visible light irradiation in the presence of H2O2. Phase pure pyrochlore Bi1.9Te0.58Fe1.52O6.87 (BTF) nanoparticles were synthesised by coprecipitation reaction and further annealing in the furnace at 570 °C for 7h. Although the BTF nanoparticles include higher amount of Fe than BNF nanoparticles and exhibit narrower band gap, the photoactivity of these nanoparticles is a bit lower than that of BNF nanoparticles. We assume that Fe at some critical concentration causes formation of mid-band states, which act as recombination centers. The same as BiOCl/BNF, the BiOCl/BTF composite is able to decolourize 100 % of the 7 mg/L MO within 2h of the visible light irradiation in the presence of H2O2. Based on the band gap determination and estimation of valence and conduction band levels, the proposed photodecolourization mechanisms are discussed. The conduction band levels of all synthesized materials lie more positively than O2/O2● redox potential (vs. negative hydrogen electrode potential), but are more close to H2O2/●OH redox potential. Thus, we assume that the photogenerated electrons form ●OH radicals, the species that induce dye decolourization under visible light irradiation. We believe that better performance of composite materials (BiOCl/BNF, BiOCl/BTF) is due to the formation of heterojunction, which facilitates the electron transfer between semiconductors, and O2 vacancy states formation in the BiOCl material.
Found in: ključnih besedah
Summary of found: ...target for the high-performance photocatalysts. To prepare nanoparticles that are not agglomerated, different synthesis methods...
Keywords: nanoparticles, pyrochlore structure, photocatalysis, visible light
Published: 26.06.2015; Views: 3867; Downloads: 88
.pdf Fulltext (7,29 MB)

2.
Microstructural features of carbon ordering during carbonization of pine wood shavings
Kateryna L. Vyshnyakova, Lyudmila N. Pereselentseva, G. S. Oleynik, L. R. Vishnyakov, A. V. Kotko, 2011, original scientific article

Found in: ključnih besedah
Summary of found: ...pyrolysis, carbon nanoparticles, microstructure, ...
Keywords: pyrolysis, carbon nanoparticles, microstructure
Published: 09.05.2017; Views: 1004; Downloads: 56
URL Fulltext (0,00 KB)

3.
Packing patterns of silica nanoparticles on surfaces of armored polystyrene latex particles
Sara Fortuna, Catheline A. L. Colard, Stefan A. F. Bon, Alessandro Troisi, 2009, original scientific article

Abstract: 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.
Found in: ključnih besedah
Keywords: packing patterns, silica, simulation, Monte Carlo, order, disorder, transition, armored particles, nanoparticles, Pickering emulsion
Published: 10.10.2016; Views: 1521; Downloads: 0
.pdf Fulltext (3,85 MB)

4.
One-pot synthesis of biocompatible silver nanoparticle composites from cellulose and keratin: characterization and antimicrobial activity
Gerald Benzi, Mladen Franko, Franja Prosenc, Chieu Ding Tran, 2016, original scientific article

Abstract: 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.
Found in: ključnih besedah
Summary of found: ...either Ag+ (in the form of Ag2O nanoparticles (NPs)) or Ag0NPs form with size of...
Keywords: Celulose, Keratin, Cmposites, Biocompatible, Ag nanoparticles, one-pot synthesis, Antibacterial, Antiviral
Published: 28.11.2016; Views: 1725; Downloads: 0
.pdf Fulltext (2,04 MB)

5.
Biotinylated Vanadium and Chromium Sulfide Nanoparticles as Probes for Colocalization of Membrane Proteins
Saim Emin, Alexandre Loukanov, 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.
Found in: ključnih besedah
Keywords: biotin-dihydrolipoic conjugate, vanadium and chromium sulfide nanoparticles, membrane proteins
Published: 02.02.2017; Views: 1673; Downloads: 0
.pdf Fulltext (581,45 KB)

6.
Biotransformation of copper oxide nanoparticles by the pathogenic fungus Botrytis cinerea
Katarina Vogel-Mikuš, Darko Makovec, Tamás Papp, Iztok Arčon, Johannes Teun van Elteren, Marjana Regvar, Eva Kovačec, 2017, original scientific article

Abstract: Two plant pathogenic fungi, Botrytis cinerea and Alternaria alternata, isolated from crop plants, were exposed to Cu in ionic (Cu2þ), microparticulate (MP, CuO) or nanoparticulate (NP, Cu or CuO) form, in solid and liquid culturing media in order to test fungal response and toxic effects of the mentioned compounds for the potential use as fungicides. B. cinerea has shown pronounced growth and lower levels of lipid peroxidation compared to A. alternata. Its higher resistance/tolerance is attributed mainly to biotransformation of CuO and Cu NPs and CuO MPs into a blue compound at the fungal/culturing media interface, recognized by Cu K-edge EXAFS analysis as Cu-oxalate complex. The pronounced activity of catechol-type siderophores and organic acid secretion in B. cinerea induce leaching and mobilization of Cu ions from the particles and their further complexation with extracellularly secreted oxalic acid. The ability of pathogenic fungus to biotransform CuO MPs and NPs hampers their use as fungicides. However the results show that B. cinerea has a potential to be used in degradation of Cu(O) nanoparticles in environment, copper extraction and purification techniques.
Found in: ključnih besedah
Keywords: copper, metal oxide nanoparticles, detoxification mechanisms, metal pollution, Cu-oxalate
Published: 23.08.2017; Views: 1049; Downloads: 0
.pdf Fulltext (1,52 MB)

7.
Photoelectrochemical Water Splitting Studies with nanostructured n and p-type semiconductor electrodes
Matjaz Valant, Saim Emin, 2017, published scientific conference contribution abstract (invited lecture)

Abstract: Photoelectrochemical water splitting has been demonstrated as a promising way to efficiently split water. Currently, solar-to-hydrogen conversion efficiency using state-of-the-art material combinations in PEC system is in the order of 7%. Fabrication of nanostructured materials with unique morphologies and compositions is an important factor to fully utilize the possibilities in this field. We will present different strategies for the preparation of nanostructured metal oxide thin films by using electrodeposition and wet-chemistry techniques. Focus will be given on the preparation of ZnO and CuO thin films where intermediate phases like Zn(OH)8Cl2.H2O and CuX (X=Br, Cl) were electrodeposited. Wet-chemistry synthesis techniques will be also explored for the preparation of nanostructured WO3 and a-Fe2O3 thin films. Especially, the hot-pyrolysis technique for the preparation of colloidal W and Fe/Fe-oxide nanoparticles will be shown. Spin-coating of W and Fe/Fe-oxide NPs onto optically conductive substrates and subsequent heat treatment of the obtained films was found to be a convenient way for the preparation of nanostructured WO3 and a-Fe2O3 thin films.
Found in: ključnih besedah
Summary of found: ...the preparation of colloidal W and Fe/Fe-oxide nanoparticles will be shown. Spin-coating of W and...
Keywords: photoelectrochemical water splitting, colloidal nanoparticles, semiconductor
Published: 24.10.2017; Views: 1242; Downloads: 0
.pdf Fulltext (1,47 MB)

8.
Facile synthesis, structure, biocompatibility and antimicrobial property of gold nanoparticle composites from cellulose and keratin
Mladen Franko, Franja Prosenc, Chieu D. Tran, 2018, original scientific article

Abstract: A novel, one-pot method was developed to synthesize gold nanoparticle composite from cellulose (CEL), wool keratin (KER) and chloroauric acid. Two ionic liquids, butylmethylimmidazolium chloride and ethylmethylimmidazolium bis(trifluoromethylsulfonyl)imide were used to dissolve CEL, KER and HAuCl4. X-ray diffraction and X-ray photoelectron results show that Au3+ was completely reduced to Au0NPs with size of (5.5 ± 1) nm directly in the composite with NaBH4. Spectroscopy and imaging results indicate that CEL and KER remained chemically intact and were homogeneously distributed in the com- posites with Au0NPs. Encapsulating Au0NPs into [CEL+KER] composite made the composite fully biocom- patible and their bactericidal capabilities were increased by the antibacterial activity of Au0NPs. Specifically, the [CEL+KER+Au0NPs] composite exhibited up to 97% and 98% reduction in growth of antibi- otic resistant bacteria such as vancomycin resistant Enterococcus faecalis and methicillin resistant Staphylococcus aureus, and was not cytotoxic to human fibroblasts. While [CEL+KER] composite is known to possess some antibacterial activity, the enhanced antibacterial observed here was due solely to added Au0NPs. These results together with our previous finding that [CEL+KER] composites can be used for con- trolled delivery of drugs clearly indicate that the [CEL+KER+Au0NPs] composites possess all required properties for successful use as dressing to treat chronic ulcerous infected wounds.
Found in: ključnih besedah
Summary of found: ...Ionic liquid Green Sustainable Polysaccharide Keratin Wound dressing Gold nanoparticles Antibiotic-resistant bacteria...
Keywords: Ionic liquid Green Sustainable Polysaccharide Keratin Wound dressing Gold nanoparticles Antibiotic-resistant bacteria
Published: 27.09.2017; Views: 1071; Downloads: 0
.pdf Fulltext (2,44 MB)

9.
Metal oxide and metal carbides thin films for photo/electrochemical water splitting studies
Saim Emin, 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 both tungsten trioxide (WO3) and tungsten carbide (W2C, WC) thin films. The preparation of WO3 thin films was achieved by spin-coating of W NPs on fluorine doped tin oxide (FTO) glass substrates and following thermal treatment in air at 500°C. The preparation of W2C and WC were done after spin-coating of W NPs on graphite substrate and following heat treatment under Ar atmosphere at 1000 and 1450°C. The obtained WO3 and W2C (e.g WC) films were used both in photo/electrochemical water splitting studies. In conclusion, we have developed a procedure for the synthesis of W NPs which can be used for the preparation of different class of materials for water splitting studies.
Found in: ključnih besedah
Summary of found: ...wet-chemistry techniques to prepare colloidal tungsten (W) nanoparticles (NPs). The synthesis of W NPs was...
Keywords: metal oxides, metal carbides, tungsten nanoparticles
Published: 09.10.2017; Views: 1387; Downloads: 0
.pdf Fulltext (364,61 KB)

10.
Tungsten carbide thin films for electrochemical water splitting studies
Hasan Okuyucu, Matjaz Valant, Ali Semerci, Cesur Altinkaya, Saim Emin, 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.
Found in: ključnih besedah
Summary of found: ...wet-chemistry techniques to prepare colloidal tungsten (W) nanoparticles (NPs). The synthesis of W NPs was...
Keywords: water splitting, nanoparticles, hot-matrix
Published: 09.10.2017; Views: 1555; Downloads: 0
.pdf Fulltext (376,30 KB)

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