Showing papers by "Vadim G. Kessler published in 2016"

Pushing the theoretical capacity limits of iron oxide anodes: capacity rise of γ-Fe2O3 nanoparticles in lithium-ion batteries

Abstract: Nanoparticles (NPs) of γ-Fe2O3 are successfully prepared via facile hydrolysis of a complex iron iodide precursor with subsequent oxidation under mild conditions When evaluated as an anode material in lithium ion half-cells, electrodes made with γ-Fe2O3 NPs exhibit excellent rate capabilities with high capacities and good coulombic efficiencies Electrodes of γ-Fe2O3 NPs initially deliver capacities of 1100 mA h g−1 at 100 mA g−1 current density and 980 mA h g−1 at 1000 mA g−1 Following an activation step of the electrodes, the capacities increase by up to ∼300 mA h g−1 while coulombic efficiencies also improve slightly At a high current density of 4000 mA g−1, a stable capacity of 770 mA h g−1 is achieved In this study, dQ/dv plots are employed to graphically illustrate the capacity breakdown of each cycle into intercalation, conversion, and extra capacity regions Upon prolonged cycling, the extra capacity region expands to yield higher capacities; this phenomenon has been attributed to both pulverization-induced particle size reduction and high-rate lithiation-induced activation processes This study concludes that γ-Fe2O3 NPs could serve as a promising anode material with comparable results to widely studied α-Fe2O3 and Fe3O4 NPs

Nanoparticle Self-Assembly Mechanisms in the Colloidal Synthesis of Iron Titanate Nanocomposite Photocatalysts for Environmental Applications

Abstract: Colloidal synthesis of iron titanate-based nanocomposites exploiting the interaction of solutions of binary oxide nanoparticles, Fe2O3 and TiO2, was investigated with respect to the pH of the reaction medium and the conditions used for the synthesis of the reactants. It has been demonstrated that while the phase composition of the products is rather analogous, involving the formation of iron titanate phases on the grain boundaries of the binary oxide particles, the morphology of the resulting aggregates can be a matter of pH control. The self-assembly mechanisms are guided by the surface charge of the particles, offering nanorod regular colloid crystal structures of altering particles with opposite initial charges at neutral pH and globular aggregates with random distribution of uniformly charged particles at low pH as revealed by DLS and high-resolution TEM studies. The produced materials demonstrated enhanced photocatalytic activity compared to the iron titanates produced by conventional techniques. Mag...

Palladium Nanoparticles: Is There a Risk for Aquatic Ecosystems?

Abstract: Nano-sized palladium (nano-Pd) is used in catalytic converters of automobiles, where it can be released into the environment by abrasion. Although these particles may subsequently be transported into surface water bodies, no data estimating their fate and toxicity in aquatic systems exists. This study characterized the particle size development of nano-Pd (advertised size ~12 nm; hydrodynamic size ~70 nm) in media with variable ionic strength (IS). Additionally, the particles' acute toxicity for daphnids and chironomids was assessed. While nano-Pd agglomerated more quickly with increasing IS, it caused only marginal effects in both test species after 96 h of exposure. After 144 h of exposure, however, an EC50 value of 1.23 mg nano-Pd/L for daphnids was determined indicating effects over the long run. When considering the relatively low environmental concentration of elemental Pd in surface waters (usually ng/L), though, this study suggests only a low aquatic risk in response to nano-Pd.

Comparing human respiratory adverse effects after acute exposure to particulate matter in conventional and particle-reduced swine building environments

Abstract: Objectives To evaluate innate immunity responses, lung function and symptoms in volunteers acutely exposed to organic dust in swine buildings after installing particle separators aimed to reduce particulate matter exposure. Methods 11 healthy participants were exposed in 2 different facilities, with and without installed particle separators, in a cross-over design including 2–3 weeks wash-out between the 2 exposures. Size, distribution and composition of particulate matter and endotoxins in the air were measured. Lung function (spirometry), bronchial responsiveness, symptoms questionnaire and markers of innate immunity in blood and nasal lavage were measured before and after the 3-hour exposures. Results The number of particles, in particular fine particles sized 0.3–0.5 µm, was reduced in the particle-separated swine building environment (PSE) compared with that in the conventional building (CE). In the PSE, headache (p=0.03) and increased body temperature (p=0.016) were less pronounced than in the CE. The expression of toll-like receptors (TLR)2 and TLR4 on blood monocytes significantly increased (p=0.016 and 0.017, respectively) while cluster of differentiation (CD)14 on neutrophils decreased (p=0.05) after exposure in the CE, yet with no difference between the 2 exposures. Compared with the conventional environment, exposure to the PSE yielded lower interleukin (IL)-6 (p=0.02) and IL-8 (p=0.04) levels in the upper respiratory tract, as assessed by nasal lavage. Conclusions Particulate matter and organic dust in the swine building were reduced after installing particle separators, which, in naive never exposed volunteers, in turn reduced adverse health effects caused by acute exposure in swine buildings compared with exposure to the conventional swine building environment.

Self-assembled SnO2 micro- and nanosphere-based gas sensor thick films from an alkoxide-derived high purity aqueous colloid precursor.

Abstract: Tin oxide is considered to be one of the most promising semiconductor oxide materials for use as a gas sensor. However, a simple route for the controllable build-up of nanostructured, sufficiently pure and hierarchical SnO2 structures for gas sensor applications is still a challenge. In the current work, an aqueous SnO2 nanoparticulate precursor sol, which is free of organic contaminants and sorbed ions and is fully stable over time, was prepared in a highly reproducible manner from an alkoxide Sn(OR)4 just by mixing it with a large excess of pure neutral water. The precursor is formed as a separate liquid phase. The structure and purity of the precursor is revealed using XRD, SAXS, EXAFS, HRTEM imaging, FTIR, and XRF analysis. An unconventional approach for the estimation of the particle size based on the quantification of the Sn-Sn contacts in the structure was developed using EXAFS spectroscopy and verified using HRTEM. To construct sensors with a hierarchical 3D structure, we employed an unusual emulsification technique not involving any additives or surfactants, using simply the extraction of the liquid phase, water, with the help of dry butanol under ambient conditions. The originally generated crystalline but yet highly reactive nanoparticles form relatively uniform spheres through self-assembly and solidify instantly. The spheres floating in butanol were left to deposit on the surface of quartz plates bearing sputtered gold electrodes, producing ready-for-use gas sensors in the form of ca. 50 μm thick sphere-based-films. The films were dried for 24 h and calcined at 300°C in air before use. The gas sensitivity of the structures was tested in the temperature range of 150-400°C. The materials showed a very quickly emerging and reversible (20-30 times) increase in electrical conductivity as a response to exposure to air containing 100 ppm of H2 or CO and short (10 s) recovery times when the gas flow was stopped.

Summary of the 3rd sol–gel conference of the CIS countries

Abstract: An overview of the conference of CIS countries “Sol–Gel Synthesis and Investigation of Inorganic Compounds, Functional Hybrid Materials, and Disperse Systems” (Sol–Gel 2014) held in the town Suzdal in September 2014, is presented.