Metal–organic frameworks (MOFs) are increasingly being investigated as electrocatalysts for the oxygen evolution reaction (OER). Despite their promising catalytic activity, many fundamental questions concerning their structure−performance relationships—especially those regarding the roles of active species—remain to be answered. Here we show the structural transformation of a Ni0.5Co0.5-MOF-74 during the OER by operando X-ray absorption spectroscopy analysis and high-resolution transmission electron microscopy imaging. We suggest that Ni0.5Co0.5OOH0.75, with abundant oxygen vacancies and high oxidation states, forms in situ and is responsible for the high OER activity observed. The ratio of Ni to Co in the bimetallic centres alters the geometric and electronic structure of as-formed active species and in turn the catalytic activity. Based on our understanding of this system, we fabricate a Ni0.9Fe0.1-MOF that delivers low overpotentials of 198 mV and 231 mV at 10 mA cm−2 and 20 mA cm−2, respectively. Metal–organic frameworks (MOFs) are increasingly being explored for electrocatalytic oxygen evolution, which is half of the water splitting reaction. Here the authors show that, under reaction conditions, mixed metal oxyhydroxides form at the nodes of bimetallic MOFs, which are highly catalytically active.

Structural transformation of highly active metal–organic framework electrocatalysts during the oxygen evolution reaction

Silver nanoparticles (AgNPs) are increasingly used as antimicrobial additives in consumer products and may have adverse impacts on organisms when they inadvertently enter ecosystems. This study investigated the uptake and toxicity of AgNPs to the common grass, Lolium multiflorum. We found that root and shoot Ag content increased with increasing AgNP exposures. AgNPs inhibited seedling growth. While exposed to 40 mg L(-1) GA-coated AgNPs, seedlings failed to develop root hairs, had highly vacuolated and collapsed cortical cells and broken epidermis and rootcap. In contrast, seedlings exposed to identical concentrations of AgNO(3) or supernatants of ultracentrifuged AgNP solutions showed no such abnormalities. AgNP toxicity was influenced by total NP surface area with smaller AgNPs (6 nm) more strongly affecting growth than did similar concentrations of larger (25 nm) NPs for a given mass. Cysteine (which binds Ag(+)) mitigated the effects of AgNO(3) but did not reduce the toxicity of AgNP treatments. X-ray spectro-microscopy documented silver speciation within exposed roots and suggested that silver is oxidized within plant tissues. Collectively, this study suggests that growth inhibition and cell damage can be directly attributed either to the nanoparticles themselves or to the ability of AgNPs to deliver dissolved Ag to critical biotic receptors.

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More than the Ions: The Effects of Silver Nanoparticles on Lolium multiflorum

pyFAI is an open-source software package designed to perform azimuthal integration and, correspondingly, two-dimensional regrouping on area-detector frames for small- and wide-angle X-ray scattering experiments. It is written in Python (with binary submodules for improved performance), a language widely accepted and used by the scientific community today, which enables users to easily incorporate the pyFAI library into their processing pipeline. This article focuses on recent work, especially the ease of calibration, its accuracy and the execution speed for integration.This article will form part of a virtual special issue of the journal, presenting some highlights of the 12th Biennial Conference on High-Resolution X-ray Diffraction and Imaging (XTOP2014).

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The fast azimuthal integration Python library: pyFAI .

Accumulation, translocation and impact of TiO2 nanoparticles in wheat (Triticum aestivum spp.): Influence of diameter and crystal phase

Foliar exposure of the crop Lactuca sativa to silver nanoparticles: Evidence for internalization and changes in Ag speciation

A multiplatform code for the analysis of energy-dispersive X-ray fluorescence spectra

Kinetics of oil saponification by lead salts in ancient preparations of pharmaceutical lead plasters and painting lead mediums

The combination of ion beam analysis techniques is particularly fruitful for the study of cultural heritage objects. For several years, the AGLAE facility of the Louvre laboratory has been implementing these techniques with an external beam. The recent set-up permits to carry out PIXE, PIGE and RBS simultaneously on the same analyzed spot with a particle beam of approximately 20 μm diameter. A new mapping system has been developed in order to provide elemental concentration maps from the PIXE and RBS spectra. This system combines the Genie2000 spectroscopy software with a homemade software that creates maps by handling acquisition with the object position. Each pixel of each PIXE and RBS maps contains the spectrum normalised by the dose. After analysing each pixel of the PIXE maps (low and high energy X-ray spectra) with the Gupixwin peak-fitting software, quantitative elemental concentrations are obtained for the major and trace elements. This paper presents the quantitative elemental maps extracted from the PIXE spectra and the development of RBS data processing for light element distribution and thin layer characterization. Examples on rock painting and lustrous ceramics will be presented.

A new mapping acquisition and processing system for simultaneous PIXE-RBS analysis with external beam

For 30 years analytical methods based on ion beams have been progressively adapted to art and archaeological issues. By allowing the analysis of artefacts in a non-invasive and non-destructive way, the external beam represents the cornerstone of this evolution. In order to reach in air specifications usually obtained under vacuum, improvements in various directions have been necessary. A large panel of gadgets and experimental arrangements have been designed such as a multi-detector set-up operating in helium atmosphere to extend the range of measured elements, a nuclear microprobe at atmospheric pressure for the study of microscopic details or a reliable beam monitoring system. In addition, specific procedures have been developed to characterise multi-layered samples (easel paintings, alteration layers) by varying either the beam energy or the impinging angle. To improve the sensitivity to trace elements in high-Z materials like metals or for analysing targets too sensitive to stand direct exposure to charged particles, a specific X-ray fluorescence set-up (PIXE-XRF) based on the production of quasi-monochromatic X-rays has been developed. Eventually, the ion beam methods usually restricted for external beams to those based on photon detection (PIXE, PIGE) have been recently extended to methods based on charged particle detection (RBS, NRA and even ERDA), opening new perspectives for determination of light elements and depth profiling. This paper makes an historical review of the adaptation of IBA methods to the study of cultural heritage.

Ph. Walter

Papers

A multiplatform code for the analysis of energy-dispersive X-ray fluorescence spectra

Kinetics of oil saponification by lead salts in ancient preparations of pharmaceutical lead plasters and painting lead mediums

A new mapping acquisition and processing system for simultaneous PIXE-RBS analysis with external beam

Review of accelerator gadgets for art and archaeology

New insight on ancient cosmetic preparation by synchrotron-based infrared microscopy