Spectroelectrochemical Signatures of Capacitive Charging and Ion Insertion in Doped Anatase Titania Nanocrystals

Solution-processed films of colloidal aliovalent niobium-doped anatase TiO₂ nanocrystals exhibit modulation of optical transmittance in two spectral regionsnear-infrared (NIR) and visible lightas they undergo progressive and reversible charging in an electrochemical cell. The Nb-TiO₂ nanocrystal film supports a localized surface plasmon resonance in the NIR, which can be dynamically modulated via capacitive charging. When the nanocrystals are charged by insertion of lithium ions, inducing a well-known structural phase transition of the anatase lattice, strong modulation of visible transmittance is observed. Based on X-ray absorption near-edge spectroscopy, the conduction electrons localize only upon lithium ion insertion, thus rationalizing the two modes of optical switching observed in a single material. These multimodal electrochromic properties show promise for application in dynamic optical filters or smart windows

Sorption and Redox Reactions of As(III) and As(V) within Secondary Mineral Coatings on Aquifer Sediment Grains

Important reactive phenomena that affect the transport and fate of many elements occur at the mineral–water interface (MWI), including sorption and redox reactions. Fundamental knowledge of these phenomena are often based on observations of ideal mineral–water systems, for example, studies of molecular scale reactions on single crystal faces or the surfaces of pure mineral powders. Much less is understood about MWI in natural environments, which typically have nanometer to micrometer scale secondary mineral coatings on the surfaces of primary mineral grains. We examined sediment grain coatings from a well-characterized field site to determine the causes of rate limitations for arsenic (As) sorption and redox processes within the coatings. Sediments were obtained from the USGS field research site on Cape Cod, MA, and exposed to synthetic contaminated groundwater solutions. Uptake of As­(III) and As­(V) into the coatings was studied with a combination of electron microscopy and synchrotron techniques to assess concentration gradients and reactive processes, including electron transfer reactions. Transmission electron microscopy (TEM) and X-ray microprobe (XMP) analyses indicated that As was primarily associated with micrometer- to submicrometer aggregates of Mn-bearing nanoparticulate goethite. As­(III) oxidation by this phase was observed but limited by the extent of exposed surface area of the goethite grains to the exterior of the mineral coatings. Secondary mineral coatings are potentially both sinks and sources of contaminants depending on the history of a contaminated site, and may need to be included explicitly in reactive transport models

Investigating Li₂NiO₂–Li₂CuO₂ Solid Solutions as High-Capacity Cathode Materials for Li-Ion Batteries

Li₂Ni_1–<i>x</i>Cu_<i>x</i>O₂ solid solutions were prepared by a solid-state method to study the correlation between composition and electrochemical performance. Cu incorporation improved the phase purity of Li₂Ni_1–<i>x</i>Cu_<i>x</i>O₂ with orthorhombic <i>Immm</i> structure, resulting in enhanced capacity. However, the electrochemical profiles suggested Cu incorporation did not prevent irreversible phase transformation during the electrochemical process, instead, it likely influenced the phase transformation upon lithium removal. By combining ex situ X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and differential electrochemical mass spectrometry (DEMS) measurements, this study elucidates the relevant phase transformation (e.g., crystal structure, local environment, and charge compensation) and participation of electrons from lattice oxygen during the first cycle in these complex oxides

Spherulitic Growth of Coral Skeletons and Synthetic Aragonite: Nature’s Three-Dimensional Printing

Coral skeletons were long assumed to have a spherulitic structure, that is, a radial distribution of acicular aragonite (CaCO₃) crystals with their <i>c</i>-axes radiating from series of points, termed centers of calcification (CoCs). This assumption was based on morphology alone, not on crystallography. Here we measure the orientation of crystals and nanocrystals and confirm that corals grow their skeletons in bundles of aragonite crystals, with their <i>c</i>-axes and long axes oriented radially and at an angle from the CoCs, thus precisely as expected for feather-like or “plumose” spherulites. Furthermore, we find that in both synthetic and coral aragonite spherulites at the nanoscale adjacent crystals have similar but not identical orientations, thus demonstrating by direct observation that even at nanoscale the mechanism of spherulite formation is non-crystallographic branching (NCB), as predicted by theory. Finally, synthetic aragonite spherulites and coral skeletons have similar angle spreads, and angular distances of adjacent crystals, further confirming that coral skeletons are spherulites. This is important because aragonite grows anisotropically, 10 times faster along the <i>c</i>-axis than along the <i>a</i>-axis direction, and spherulites fill space with crystals growing almost exclusively along the <i>c</i>-axis, thus they can fill space faster than any other aragonite growth geometry, and create isotropic materials from anisotropic crystals. Greater space filling rate and isotropic mechanical behavior are key to the skeleton’s supporting function and therefore to its evolutionary success. In this sense, spherulitic growth is Nature’s 3D printing

Speciation of Zn in Blast Furnace Sludge from Former Sedimentation Ponds Using Synchrotron X‑ray Diffraction, Fluorescence, and Absorption Spectroscopy

Blast furnace sludge (BFS), an industrial waste generated in pig iron production, typically contains high contents of iron and various trace metals of environmental concern, including Zn, Pb, and Cd. The chemical speciation of these metals in BFS is largely unknown. Here, we used a combination of synchrotron X-ray diffraction, micro-X-ray fluorescence, and X-ray absorption spectroscopy at the Zn K-edge for solid-phase Zn speciation in 12 BFS samples collected on a former BFS sedimentation pond site. Additionally, one fresh BFS was analyzed for comparison. We identified five major types of Zn species in the BFS, which occurred in variable amounts: (1) Zn in the octahedral sheets of phyllosilicates, (2) Zn sulfide minerals (ZnS, sphalerite, or wurtzite), (3) Zn in a KZn–ferrocyanide phase (K₂Zn₃[Fe­(CN)₆]₂·9H₂O), (4) hydrozincite (Zn₅(OH)₆(CO₃)₂), and (5) tetrahedrally coordinated adsorbed Zn. The minerals franklinite (ZnFe₂O₄) and smithsonite (ZnCO₃) were not detected, and zincite (ZnO) was detected only in traces. The contents of ZnS were positively correlated with the total S contents of the BFS. Similarly, the abundance of the KZn–ferrocyanide phase was closely correlated with the total CN contents, with the stoichiometry suggesting this as the main cyanide phase. This study provides the first quantitative Zn speciation in BFS deposits, which is of great relevance for environmental risk assessment, the development of new methods for recovering Zn and Fe from BFS, and potential applications of BFS as sorbent materials in wastewater treatment

X-Ray Fluorescence Imaging: A New Tool for Studying Manganese Neurotoxicity

<div><p>The neurotoxic effect of manganese (Mn) establishes itself in a condition known as <em>manganism</em> or Mn induced parkinsonism. While this condition was first diagnosed about 170 years ago, the mechanism of the neurotoxic action of Mn remains unknown. Moreover, the possibility that Mn exposure combined with other genetic and environmental factors can contribute to the development of Parkinson's disease has been discussed in the literature and several epidemiological studies have demonstrated a correlation between Mn exposure and an elevated risk of Parkinson's disease. Here, we introduce X-ray fluorescence imaging as a new quantitative tool for analysis of the Mn distribution in the brain with high spatial resolution. The animal model employed mimics deficits observed in affected human subjects. The obtained maps of Mn distribution in the brain demonstrate the highest Mn content in the globus pallidus, the thalamus, and the substantia nigra pars compacta. To test the hypothesis that Mn transport into/distribution within brain cells mimics that of other biologically relevant metal ions, such as iron, copper, or zinc, their distributions were compared. It was demonstrated that the Mn distribution does not follow the distributions of any of these metals in the brain. The majority of Mn in the brain was shown to occur in the mobile state, confirming the relevance of the chelation therapy currently used to treat Mn intoxication. In cells with accumulated Mn, it can cause neurotoxic action by affecting the mitochondrial respiratory chain. This can result in increased susceptibility of the neurons of the globus pallidus, thalamus, and substantia nigra pars compacta to various environmental or genetic insults. The obtained data is the first demonstration of Mn accumulation in the substantia nigra pars compacta, and thus, can represent a link between Mn exposure and its potential effects for development of Parkinson's disease.</p> </div

An Operando Investigation of (Ni–Fe–Co–Ce)O_<i>x</i> System as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is a critical component of industrial processes such as electrowinning of metals and the chlor-alkali process. It also plays a central role in the development of a renewable energy field for generation a solar fuels by providing both the protons and electrons needed to generate fuels such as H₂ or reduced hydrocarbons from CO₂. To improve these processes, it is necessary to expand the fundamental understanding of catalytically active species at low overpotential, which will further the development of electrocatalysts with high activity and durability. In this context, performing experimental investigations of the electrocatalysts under realistic working regimes (i.e., under operando conditions) is of crucial importance. Here, we study a highly active quinary transition-metal-oxide-based OER electrocatalyst by means of operando ambient-pressure X-ray photoelectron spectroscopy and X-ray absorption spectroscopy performed at the solid/liquid interface. We observe that the catalyst undergoes a clear chemical-structural evolution as a function of the applied potential with Ni, Fe, and Co oxyhydroxides comprising the active catalytic species. While CeO₂ is redox inactive under catalytic conditions, its influence on the redox processes of the transition metals boosts the catalytic activity at low overpotentials, introducing an important design principle for the optimization of electrocatalysts and tailoring of high-performance materials

XRF imaging of the substantia nigra of control and treated samples.

<p>XRF images of Mn (<b>A</b>) and Fe (<b>B</b>) for treated and control samples. Note that the maximum Mn intensity for the control sample is 30% of the treated maximum intensity. Numbers given are in µg/g. (<b>C</b>) Tri-colored image of the SN where red, green, and blue represent Mn, Fe, and Cu respectively (same scale for Mn). Scale bar represents a length of 1 mm. (<b>D</b>) Confocal images of tyrosine hydroxylase stained SN area of adjunct sections recorded in identical experimental conditions.</p

Distribution and Chemical Speciation of Arsenic in Ancient Human Hair Using Synchrotron Radiation

Pre-Columbian populations that inhabited the Tarapacá mid river valley in the Atacama Desert in Chile during the Middle Horizon and Late Intermediate Period (AD 500–1450) show patterns of chronic poisoning due to exposure to geogenic arsenic. Exposure of these people to arsenic was assessed using synchrotron-based elemental X-ray fluorescence mapping, X-ray absorption spectroscopy, X-ray diffraction and Fourier transform infrared spectromicroscopy measurements on ancient human hair. These combined techniques of high sensitivity and specificity enabled the discrimination between endogenous and exogenous processes that has been an analytical challenge for archeological studies and criminal investigations in which hair is used as a proxy of premortem metabolism. The high concentration of arsenic mainly in the form of inorganic As­(III) and As­(V) detected in the hair suggests chronic arsenicism through ingestion of As-polluted water rather than external contamination by the deposition of heavy metals due to metallophilic soil microbes or diffusion of arsenic from the soil. A decrease in arsenic concentration from the proximal to the distal end of the hair shaft analyzed may indicate a change in the diet due to mobility, though chemical or microbiologically induced processes during burial cannot be entirely ruled out

Selenium Hyperaccumulator Plants <em>Stanleya pinnata</em> and <em>Astragalus bisulcatus</em> Are Colonized by Se-Resistant, Se-Excluding Wasp and Beetle Seed Herbivores

<div><p>Selenium (Se) hyperaccumulator plants can concentrate the toxic element Se up to 1% of shoot (DW) which is known to protect hyperaccumulator plants from generalist herbivores. There is evidence for Se-resistant insect herbivores capable of feeding upon hyperaccumulators. In this study, resistance to Se was investigated in seed chalcids and seed beetles found consuming seeds inside pods of Se-hyperaccumulator species <em>Astragalus bisulcatus</em> and <em>Stanleya pinnata.</em> Selenium accumulation, localization and speciation were determined in seeds collected from hyperaccumulators in a seleniferous habitat and in seed herbivores. <em>Astragalus bisulcatus</em> seeds were consumed by seed beetle larvae (<em>Acanthoscelides fraterculus</em> Horn, Coleoptera: Bruchidae) and seed chalcid larvae (<em>Bruchophagus mexicanus</em>, Hymenoptera: Eurytomidae). <em>Stanleya pinnata</em> seeds were consumed by an unidentified seed chalcid larva. Micro X-ray absorption near-edge structure (µXANES) and micro-X-Ray Fluorescence mapping (µXRF) demonstrated Se was mostly organic C-Se-C forms in seeds of both hyperaccumulators, and <em>S. pinnata</em> seeds contained ∼24% elemental Se. Liquid chromatography–mass spectrometry of Se-compounds in <em>S. pinnata</em> seeds detected the C-Se-C compound seleno-cystathionine while previous studies of <em>A. bisulcatus</em> seeds detected the C-Se-C compounds methyl-selenocysteine and γ-glutamyl-methyl-selenocysteine. Micro-XRF and µXANES revealed Se ingested from hyperaccumulator seeds redistributed throughout seed herbivore tissues, and portions of seed C-Se-C were biotransformed into selenocysteine, selenocystine, selenodiglutathione, selenate and selenite. <em>Astragalus bisulcatus</em> seeds contained on average 5,750 µg Se g⁻¹, however adult beetles and adult chalcid wasps emerging from <em>A. bisulcatus</em> seed pods contained 4–6 µg Se g⁻¹. <em>Stanleya pinnata</em> seeds contained 1,329 µg Se g⁻¹ on average; however chalcid wasp larvae and adults emerging from <em>S. pinnata</em> seed pods contained 9 and 47 µg Se g⁻¹. The results suggest Se resistant seed herbivores exclude Se, greatly reducing tissue accumulation; this explains their ability to consume high-Se seeds without suffering toxicity, allowing them to occupy the unique niche offered by Se hyperaccumulator plants.</p> </div