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Stable concentrated aqueous dispersions of silver nanoparticles of narrow size distribution were prepared by reducing silver nitrate solutions with ascorbic acid in the presence of Daxad 19 (sodium salt of a high-molecular-weight ...
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Stable concentrated aqueous dispersions of silver nanoparticles of narrow size distribution were prepared by reducing silver nitrate solutions with ascorbic acid in the presence of Daxad 19 (sodium salt of a high-molecular-weight naphthalene sulfonate formaldehyde condensate) as stabilizing agent. The latter has ecellent ability to preent the aggregation of nanosize silver at high ionic strength and high concentration of metal (up to 0.3 mol dm~(-3)). The presence of the dispersing agent on the surface of silver particles was confirmed by ATR-FTIR spectroscopy and electrokinetic measurements, explaining both the negative charge over the entire pH range and the electrosteric effect responsible for their long-term stawbility. The other experimental conditions, i.e., the pH of the reacting solutions, the concentration of the stabilizing agent, and the metal/dispersant ratio, also have a significant impact on the size and stability of these dispersions. The final nanosize silver can be obtained as drived powder, and can be fully redispersed in deionized water by sonication.
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Photochemical processes in thin surface layers of solutions of compounds of the copper subgroup elements leading to the formation of dispersed metal particles on the surface of dielectrics are investigated. It is shown that disper...
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Photochemical processes in thin surface layers of solutions of compounds of the copper subgroup elements leading to the formation of dispersed metal particles on the surface of dielectrics are investigated. It is shown that dispersed particles of elemental gold are formed on dielectrics moistened with AuCl3 solution and exposed to sunlight. At the same time, there is no need to use any chemical reducing agents. On cotton fabrics moistened with solutions of AgNO3, CuBr2, when exposed to sunlight, silver and copper monohalides are formed, respectively. These processes take place with the participation of terminal cellulose molecules and also do not require the use of chemical reducing agents. In addition, it was found that copper monohalides can be converted into elemental copper particles by a photochemical reaction involving ascorbic acid. Examples of metallization of a number of dielectrics using photochemical activation using sunlight are given.
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Silver (Ag) undergoes a complex and dynamic Ag~+/Ag~0 cycle under environmental conditions. The Ag~+ → Ag nanoparticles (AgNPs) transformation due to the combined actions of sunlight, O_2, and dissolved organic matter has been a ...
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Silver (Ag) undergoes a complex and dynamic Ag~+/Ag~0 cycle under environmental conditions. The Ag~+ → Ag nanoparticles (AgNPs) transformation due to the combined actions of sunlight, O_2, and dissolved organic matter has been a well-known environmental phenomenon. In this study, we indicate that this process may be accompanied by a pronounced accumulation of Ag(0) single atoms (Ag-SAs) on the minerals' surfaces. According to spherical aberration-corrected scanning transmission electron microscopy and high-energy-resolution X-ray adsorption fine structure analyses, humic acid (HA) and phenol (PhOH) can induce Ag-SAs accumulation, whereas oxalic acid causes only AgNPs deposition. Ag-SAs account for more than 20 wt % of total Ag(0) on the γ-Al_2O_3 surfaces during HA- and PhOH-mediated photolysis processes. HA also causes Ag-SAs to accumulate on two other prevalent soil minerals, SiO_2 and Fe_2O_3 and the fractions of Ag-SAs are about 15 wt %. Our mechanism studies suggest that a phenolic molecule acts as a reducing agent of Ag~+ and a stabilizer of Ag-SAs, protecting Ag-SAs against autocatalytic nucleation.
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We report on a stabilization effect on the structure and activity of Ag/Al2O3 for the selective catalytic reduction (SCR) of NO_x with CH4 imparted by the presence of SO2 in the exhaust gas mixture. The reaction is carried out at ...
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We report on a stabilization effect on the structure and activity of Ag/Al2O3 for the selective catalytic reduction (SCR) of NO_x with CH4 imparted by the presence of SO2 in the exhaust gas mixture. The reaction is carried out at temperature above 600 °C to keep the surface partially free of sulfates. In SO2-free gases, catalyst deactivation is fast and measurable at these temperatures. Time-resolved TEM analyses of used samples have determined that deactivation is due to sintering of silver from well-dispersed clusters to nanoparticles to micrometer-size particles with time-on-stream at 625 °C. However, sintering of silver was dramatically suppressed by the presence of SO2 in the reaction gas mixture. The structural stabilization by SO2 was accompanied by stable catalyst activity for the NO reduction to N2. The direct oxidation of methane was suppressed, thus the methane selectivity was improved in SO2-laden gas mixtures. In tests with high-content silver alumina with some of the silver present in metallic form, an increase in the SCR activity was found in SO2-containing gas mixtures. This is attributed to redispersion of the silver particles by SO2, an unexpected finding. The catalyst performance was reversible over many cycles of operation at 625 °C with the SO2 switched on and off in the gas mixture.
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Dispersions of colloidal silver have been prepared by the reduction of silver nitrate, with different reductants in the presence of various stabilising agents. Aging these dispersions at room temperature for 2 h yielded particles ...
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Dispersions of colloidal silver have been prepared by the reduction of silver nitrate, with different reductants in the presence of various stabilising agents. Aging these dispersions at room temperature for 2 h yielded particles with average sizes ranging from 1 nm up to 6 mu m and with various shapes like spheres, plates, needles or leafs. Reducing and stabilising agents were found to control the final particle sizes and shapes. The diversity of morphologies of the silver particles were studied by using electron microscopy. Thermogravimetry, powder X-ray diffraction (XRD) and UV/VIS spectroscopy were carried out for further characterisation. (c) 2005 Elsevier B.V. All rights reserved.
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Slow lorises are a cryptic species complex, and thus genetic markers are needed to identify distinct evolutionary lineages or species. We examined the nucleolus organizer regions (NORs) of Bengal slow lorises (Nycticebus bengalens...
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Slow lorises are a cryptic species complex, and thus genetic markers are needed to identify distinct evolutionary lineages or species. We examined the nucleolus organizer regions (NORs) of Bengal slow lorises (Nycticebus bengalensis) using FISH with 18S rDNA (rDNA-FISH) and silver nitrate staining (Ag-NOR stain). Ten individuals of the putatively single species N. bengalensis showed higher variability in localization than 3 other congeners, though their overall karyotypes were similar. The rDNA-FISH analysis detected a total of 18 loci, in contrast to previous studies of other slow loris species that revealed far fewer (6-10) loci. Eight of the 18 loci detected in the present analysis were found to be semi-stable localizations at 4 different chromosomes, while 10 were found to be unstable localizations at 5 other chromosomes. The semi-stable locations showed occasional presence/absence of variations for rDNA-FISH, and unstable locations were polymorphic among individuals, contributing to the higher variability of NORs in this taxon. We hypothesize that the larger numbers of rDNA loci found in N. bengalensis were introduced by genomic dispersion through ectopic recombination in association with terminal regions including rDNA. Such differences are potentially very powerful chromosomal markers to be used in species identification and conservation. (C) 2016 S. Karger AG, Basel
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The detection of trace elements of silver in refined copper based on the portable energy dispersive X-ray fluorescence spectrometer was disturbed severely by pulse pile-up, so quantitative analysis had a high method detection limi...
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The detection of trace elements of silver in refined copper based on the portable energy dispersive X-ray fluorescence spectrometer was disturbed severely by pulse pile-up, so quantitative analysis had a high method detection limit and low accuracy. A new approach was provided to reduce the appearance of the pulse pile-up and lower the detection limit. A robust quantitative model was established. The coefficient of determination R~2 of the model was lifted to 0.9927 from 0.9338; the detection limit was reduced to 0.0034 wt%. This model can be used in the metallurgical industry, power plants, and the study of micro-structure enhancement mechanisms.
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The present study focused on development of a robust point-of-use (POU) water disinfection device employing immobilized silver nanoparticles (AgNPs) for water disinfection in continuous flow through mode. Glass capillary tubes fun...
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The present study focused on development of a robust point-of-use (POU) water disinfection device employing immobilized silver nanoparticles (AgNPs) for water disinfection in continuous flow through mode. Glass capillary tubes functionalized with positively charged amino groups using silane as the cross-linking agent facilitated the immobilization of citrate stabilized AgNPs. A fixed bed reactor (FBR) packed with these AgNP immobilized glass substrate was used for conducting POU water disinfection. The effect of various parameters such as, flow rate, initial concentration of bacteria and bed volume on disinfection performance of the device was evaluated. The total volume of water treated at breakpoint was found to improve with increase in flow rate and 2596-5172 bed volumes of water could be disinfected under the various conditions tested, i.e., empty bed contact lime (EBCT) 0.29 to 5.8 min. Silver leaching studied under various operating conditions revealed minimal release of silver (<100 mu g/l) in treated water over time throughout the duration of the studies. Plug flow reactor with dispersion (PFDR) model with open boundary condition showed good fit to the E-curve generated by pulse input of chloride tracer and revealed significant dispersion in the FBR. Antibacterial material exhaustion rate (AER) was significantly affected by the EBCT, empty bed volume of the FBR, and load of bacteria in the influent. (C) 2019 Elsevier B.V. All rights reserved.
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Absorbing and emitting optical properties of a spherical plasmonic nanoantenna are described in terms of the size dependent resonance frequencies and damping rates of the multipolar surface plasmons (SP). We provide the plasmon si...
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Absorbing and emitting optical properties of a spherical plasmonic nanoantenna are described in terms of the size dependent resonance frequencies and damping rates of the multipolar surface plasmons (SP). We provide the plasmon size characteristics for gold and silver spherical particles up to the large size retardation regime where the plasmon radiative damping is significant. We underline the role of the radiation damping in comparison with the energy dissipation damping in formation of receiving and transmitting properties of a plasmonic particle. The size dependence of both: the multipolar SP resonance frequencies and corresponding damping rates can be a convenient tool in tailoring the characteristics of plasmonic nanoantennas for given application. Such characteristics enable to control an operation frequency of a plasmonic nanoantenna and to change the operation range from the spectrally broad to spectrally narrow and vice versa. It is also possible to switch between particle receiving (enhanced absorption) and emitting (enhanced scattering) abilities. Changing the polarization geometry of observation it is possible to effectively separate the dipole and the quadrupole plasmon radiation from all the non-plasmonic contributions to the scattered light.
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Energy Dispersive X-Ray Fluorescence (EDXRF) is a non-destructive analytical method used to solve problems involving nutritional, mineral, and toxic chemical elements. It is very common in the customization and commerce of jewelry...
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Energy Dispersive X-Ray Fluorescence (EDXRF) is a non-destructive analytical method used to solve problems involving nutritional, mineral, and toxic chemical elements. It is very common in the customization and commerce of jewelry. EDXRF depends on recording spectral lines from the irradiation of isotopes. After a brief review of the interactions of the ions Ca2+, Zn2+, P, Au3+, and Ag+ along with the results of the current study it was revealed that the methodology, when used in a semi-quantitative approach, can successfully identify all elements present in a whalebone sample collected from Santa Catarina Island (Brazil). This article serves as an example to explain the molecular reactions of Ca2+ and the concentration of elements: Cl-, Zn2+, Br, Fe, Mn, Ca, K, S, P, and Si. It was proposed initially to evaluate spectral lines of Ca2+ found in the whalebone (biomarker). The model was then further expanded to explore Ca2+ and its relationships to the intra- and extracellular environments, where the plasma membrane Ca2+-pump (PMCA) is responsible for Ca2+ ejection in most eukaryotic, excitable cells as, eg, in the cardiac tissue with a Na/Ca exchanger. The certified Road Dust (BCR-723, which is in prominence among the reference materials used) could be applied to samples of dust, soils, sediments, fossil fuel, ceramic, and bio-ceramic in general. With the aid of a matching matrix, it has been shown that EDXRF can function even with samples of Au3+ and Ag+. The results with certified reference samples of Road Dust (BCR-723) and its standards serve as a basis for studies of catalyst supports, an eg aluminum oxide containing titanium, erbium, lanthanum, and other elements, and as a model of charged ions.
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