Depth-Dependent Scanning Photoelectron Microspectroscopy Unravels the Mechanism of Dynamic Pattern Formation in Alloy Electrodeposition

Fascinating spatiotemporal patterns forming during the electrodeposition of some alloys have attracted the interest of the scientific communities dealing with electrochemical materials science and dynamic processes. Notwithstanding extensive experimental work and recently achieved theoretical insights, several aspects of the physical chemistry of these dynamic structures are still elusive. In particular, the analytical methods employed so far to characterize these structures invariably failed to pinpoint any chemical or structural patterns correlated to those perceived by the naked eye or with a light microscope. In this work, we have made systematic use of the extreme surface sensitivity provided by synchrotron-based scanning photoelectron microspectroscopy, combined with progressive erosion by precisely controlled Ar⁺ sputtering, to achieve quantitative 3D understanding of the compositional and chemical-state distribution of an Ag–In electrodeposited layer, following the key elements Ag, In, and O. The results revealed that the pattern is present only in the topmost region (ca. 100 nm) of the layer and exhibits a regular distribution of the alloying elements in certain chemical states. Specifically, pattern formation in Ag–In electrodeposits is crucially controlled by the space distribution of surface In³⁺ oxi-/hydroxides, deriving from reaction-diffusion processes taking place during alloy growth, and this pattern disappears in depth because of the delayed reduction of In³⁺ present in this film to elemental In, followed by intermetallic formation

Quasi-in-Situ Single-Grain Photoelectron Microspectroscopy of Co/PPy Nanocomposites under Oxygen Reduction Reaction

This paper reports an investigation into the aging of pyrolyzed cobalt/polypyrrole (Co/PPy) oxygen reduction reaction (ORR) electrocatalysts, based on quasi-in-situ photoelectron microspectroscopy. The catalyst precursor was prepared by potentiostatic reverse-pulse coelectrodeposition from an acetonitrile solution on graphite. Accelerated aging was obtained by quasi-in-situ voltammetric cycling in an acidic electrolyte. Using photoelectron imaging and microspectroscopy of single Co/PPy grains at a resolution of 100 nm, we tracked the ORR-induced changes in the morphology and chemical state of the pristine material, consisting of uniformly distributed ∼20 nm nanoparticles, initially consisting of a mixture of Co­(II) and Co­(III) oxidation states in almost equal amounts. The evolution of the Co 2p, O 1s, and N 1s spectra revealed that the main effects of aging are a gradual loss of the Co present at the surface and the reduction of Co­(III) to Co­(II), accompanied by the emergence and growth of a N 1s signal, corresponding to electrocatalytically active C–N sites

Effect of Ingested Tungsten Oxide (WO_<i>x</i>) Nanofibers on Digestive Gland Tissue of Porcellio scaber (Isopoda, Crustacea): Fourier Transform Infrared (FTIR) Imaging

Tungsten nanofibers are recognized as biologically potent. We study deviations in molecular composition between normal and digestive gland tissue of WO_<i>x</i> nanofibers (nano-WO_<i>x</i>) fed invertebrate Porcellio scaber (Iosopda, Crustacea) and revealed mechanisms of nano-WO_<i>x</i> effect <i>in vivo</i>. Fourier Transform Infrared (FTIR) imaging performed on digestive gland epithelium was supplemented by toxicity and cytotoxicity analyses as well as scanning electron microscopy (SEM) of the surface of the epithelium. The difference in the spectra of the Nano-WO_<i>x</i> treated and control cells showed up in the central region of the cells and were related to lipid peroxidation, and structural changes of nucleic acids. The conventional toxicity parameters failed to show toxic effects of nano-WO_<i>x</i>, whereas the cytotoxicity biomarkers and SEM investigation of digestive gland epithelium indicated sporadic effects of nanofibers. Since toxicological and cytological measurements did not highlight severe effects, the biochemical alterations evidenced by FTIR imaging have been explained as the result of cell protection (acclimation) mechanisms to unfavorable conditions and indication of a nonhomeostatic state, which can lead to toxic effects

Media 1: Conformation sequence recovery of a non-periodic object from a diffraction-before-destruction experiment

Originally published in Optics Express on 07 April 2014 (oe-22-7-8085

Cellular Internalization of Dissolved Cobalt Ions from Ingested CoFe₂O₄ Nanoparticles: In Vivo Experimental Evidence

With a model invertebrate animal, we have assessed the fate of magnetic nanoparticles in biologically relevant media, i.e., digestive juices. The toxic potential and the internalization of such nanoparticles by nontarget cells were also examined. The aim of this study was to provide experimental evidence on the formation of Co²⁺, Fe²⁺, and Fe³⁺ ions from CoFe₂O₄ nanoparticles in the digestive juices of a model organism. Standard toxicological parameters were assessed. Cell membrane stability was tested with a modified method for measurement of its quality. Proton-induced X-ray emission and low energy synchrotron radiation X-ray fluorescence were used to study internalization and distribution of Co and Fe. Co²⁺ ions were found to be more toxic than nanoparticles. We confirmed that Co²⁺ ions accumulate in the hepatopancreas, but Fe^<i>n</i>+ ions or CoFe₂O₄ nanoparticles are not retained in vivo. A model biological system with a terrestrial isopod is suited to studies of the potential dissolution of ions and other products from metal-containing nanoparticles in biologically complex media

Cellular Internalization of Dissolved Cobalt Ions from Ingested CoFe₂O₄ Nanoparticles: In Vivo Experimental Evidence

With a model invertebrate animal, we have assessed the fate of magnetic nanoparticles in biologically relevant media, i.e., digestive juices. The toxic potential and the internalization of such nanoparticles by nontarget cells were also examined. The aim of this study was to provide experimental evidence on the formation of Co²⁺, Fe²⁺, and Fe³⁺ ions from CoFe₂O₄ nanoparticles in the digestive juices of a model organism. Standard toxicological parameters were assessed. Cell membrane stability was tested with a modified method for measurement of its quality. Proton-induced X-ray emission and low energy synchrotron radiation X-ray fluorescence were used to study internalization and distribution of Co and Fe. Co²⁺ ions were found to be more toxic than nanoparticles. We confirmed that Co²⁺ ions accumulate in the hepatopancreas, but Fe^<i>n</i>+ ions or CoFe₂O₄ nanoparticles are not retained in vivo. A model biological system with a terrestrial isopod is suited to studies of the potential dissolution of ions and other products from metal-containing nanoparticles in biologically complex media