Arsenate Incorporation in Gypsum Probed by Neutron, X-ray Scattering and Density Functional Theory Modeling

International audienceThe ability of gypsum, a common sulfate mineral, to host arsenic atoms in its crystalline structure, is demonstrated through experimental structural studies of the solid solutions formed upon synthetic coprecipitation of gypsum (CaSO4 ·2H2O) and arsenic. Neutron and X-ray diffraction methods show an enlargement of the gypsum unit cell proportional to the concentration of arsenic in the solids and to the pH solution value. The substitution of sulfate ions (SO42-) by arsenate ions is shown to be more likely under alkaline conditions, where the HAsO42- species predominates. A theoretical Density Functional Theory model of the arsenicdoped gypsum structure reproduces the experimental volume expansion. Extended X-ray Absorption Fine Structure (EXAFS) measurements of the local structure around the arsenic atom in the coprecipitated solids confirm solid state substitution and allow some refinement of the local structure, corroborating the theoretical structure found in the simulations. The charge redistribution within the structure upon substitutions of either the protonated or the unprotonated arsenate species studied by means of Mulliken Population Analyses demonstrates an increase in the covalency in the interaction between Ca2+ and AsO4 3-, whereas the interaction between Ca2+ and HAsO4 2- remains predominantly ionic

Arsenic uptake by gypsum and calcite: Modeling and probing by neutron and x-ray scattering

Here we report on two structural studies performed on As-doped gypsum (CaSO4 2H2O) and calcite (CaCO3), using neutron (D20-ILL) and x-ray (ID11-ESRF) diffraction data and EXAFS (BM8-ESRF). The aim of this study is to determine whether As gets into the bulk of gypsum and calcite structures or is simply adsorbed on the surface. Different mechanisms of substitution are used as hypotheses. The combined Rietveld analysis of neutron and x-ray diffraction data shows an expansion of the unit cell volume proportional to the As concentration within the samples. DFT-based simulations confirm the increase of the unit cell volume proportional to the amount of carbonate or sulphate groups substituted. Interpolation of the experimental Rietveld data allows us to distinguish As substituted within the structure from that adsorbed on the surface of both minerals.Comment: Proceedings of the Eighth International Conference on Neutron Scatterin

A Teatro con INAF - Il Portfolio degli spettacoli dell’Istituto Nazionale di Astrofisica

A dicembre 2020, il Gruppo Storie dell’Istituto Nazionale di Astrofisica (INAF) ha pubblicato insieme al magazine di Didattica e Divulgazione dell’Ente, EduINAF, il Portfolio degli spettacoli dell’INAF. Il Portfolio è il risultato di un’accurata ricognizione in collaborazione con i referenti degli stessi ed è unico nel suo genere per un Ente di ricerca. Comprende una trentina di spettacoli, a tema astrofisico o scientifico, prodotti negli anni dal personale INAF in autonomia o in collabora-zione con realtà professionali. Nel Portfolio, ogni spettacolo è descritto in una scheda informativa e la fruizione è resa immediata grazie a filtri appositi. Il Portfolio è man mano aggiornato per meglio rispondere alle esigenze e curiosità del pubblico in cerca di approcci non tradizionali nell’esplorazione dell’astronomia e della ricerca in generale. Ad accompagnare il Portfolio, un breve video per la disseminazione sui canali social e un segnalibro dedicato, in preparazione, da offrire in incontri con scuole e in eventi con il pubblico. Grazie alla visione d’insieme offerta dal Portfolio, nell’Ente sono nate valutazioni per massimizzare la visibilità degli spettacoli tramite l’organizzazione di un ‘Festival INAF diffuso’. In questo report descriviamo il Portfolio, il suo contesto, le criticità riscontrate e i progetti futuri

Etude des propriétés structurelles locales des matériaux magnétorésistifs

The aim of this work is to give an exhaustive characterization ofthe local structure for two class of compounds: sodium dopedlanthanum manganites and tungsten doped iron-molybdenumdouble-perovskites. Both class of materials usually behave asconductors in the ferromagnetic phase and undergo ametal-to-insulator transition, associated with aferromagnetic-to-paramagnetic(antiferromagnetic) transition, uponvarying the temperature or the doping level. It is widely acceptedthat in manganites, as well as in double-perovskites, transportproperties are strongly influenced by the local structure (bondlengths and angles) around key sites, occupied by magnetic ions. Forthis reason the X-ray absorption spectroscopy (XAS), being sensitiveto the local order around the absorber atom, is the more suitabletechnique to study such compounds. In this work, the local structureof Na-doped manganites in the form of thin films has been studied asa function of the film thickness, while, bulk samples of tungstendoped iron-molybdenum double perovskite series have beeninvestigated to characterize the local structure as a function ofthe doping level and to better understand the nature of themetal-to-insulator transition. It was necessary to develop a TEYdetector. which realization was challenging from a technical pointof view and it required an extensive theoretical and technical work.X-ray absorption measurements were done at the Italian beam line fordiffraction and absorption (GILDA-BM08) at the European SynchrotronRadiation Facility (ESRF) of Grenoble (France).L'objectif de cet étude est de donner une caractérisation complètede la structure locale de deux classes de composés : les manganitesde lanthane droguées avec du sodium et les doubles perovskites deferro-molybdène droguées avec du tungstène. Les deux classes secomportent, en général comme de conducteurs dans leur phaseferromagnétique et, suivant variations de température ou de dopage,ils subissent une transition métal-isolant à laquelle il fautassocier une transitionferromagnétique-paramagnétique(antiferromagnétique). En effet, ilest tout à fait accepté que aussi bien dans les manganites, que dansles perovskites doubles, les propriétés de transport sontinfluencées d'une façon importante par la structure locale (longueuret angle de liaison) autour des sites clés occupés par des ionsmagnétiques. Pour cette raison la spectroscopie d'absorption derayon X, en étant sensible à l'ordre locale autour de l'atomeabsorbeur, constitue la technique la plus adaptée pour l'étude deces composés. La structure locale de film fins de manganite droguéesavec du sodium a été étudiée en fonction de l'épaisseur des film.Des échantillons de poudre de perovskites double droguées avectungstène ont été étudiées pour en caractériser la structure localeen fonction du dopage et pour chercher de comprendre la nature de latransition métal-isolant. Il a été nécessaire de développer undétecteur d'électrons. La réalisation de cet instrument s'est révéléun défi du point de vue technique et il a demandé une quantité detravail aussi bien sur la plan pratique que théorique. Les mesuresd'absorption de rayon-X ont été effectuées à la ligne de lumièreitalienne pour la diffraction et l'absorption (GILDA-BM8) àl'Installation Européenne de Rayonnement de Synchrotron (ESRF) deGrenoble (France)

Etude des propriétés structurelles locales des matériaux magnétorésistifs

The aim of this work is to give an exhaustive characterization ofthe local structure for two class of compounds: sodium dopedlanthanum manganites and tungsten doped iron-molybdenumdouble-perovskites. Both class of materials usually behave asconductors in the ferromagnetic phase and undergo ametal-to-insulator transition, associated with aferromagnetic-to-paramagnetic(antiferromagnetic) transition, uponvarying the temperature or the doping level. It is widely acceptedthat in manganites, as well as in double-perovskites, transportproperties are strongly influenced by the local structure (bondlengths and angles) around key sites, occupied by magnetic ions. Forthis reason the X-ray absorption spectroscopy (XAS), being sensitiveto the local order around the absorber atom, is the more suitabletechnique to study such compounds. In this work, the local structureof Na-doped manganites in the form of thin films has been studied asa function of the film thickness, while, bulk samples of tungstendoped iron-molybdenum double perovskite series have beeninvestigated to characterize the local structure as a function ofthe doping level and to better understand the nature of themetal-to-insulator transition. It was necessary to develop a TEYdetector. which realization was challenging from a technical pointof view and it required an extensive theoretical and technical work.X-ray absorption measurements were done at the Italian beam line fordiffraction and absorption (GILDA-BM08) at the European SynchrotronRadiation Facility (ESRF) of Grenoble (France).L'objectif de cet étude est de donner une caractérisation complètede la structure locale de deux classes de composés : les manganitesde lanthane droguées avec du sodium et les doubles perovskites deferro-molybdène droguées avec du tungstène. Les deux classes secomportent, en général comme de conducteurs dans leur phaseferromagnétique et, suivant variations de température ou de dopage,ils subissent une transition métal-isolant à laquelle il fautassocier une transitionferromagnétique-paramagnétique(antiferromagnétique). En effet, ilest tout à fait accepté que aussi bien dans les manganites, que dansles perovskites doubles, les propriétés de transport sontinfluencées d'une façon importante par la structure locale (longueuret angle de liaison) autour des sites clés occupés par des ionsmagnétiques. Pour cette raison la spectroscopie d'absorption derayon X, en étant sensible à l'ordre locale autour de l'atomeabsorbeur, constitue la technique la plus adaptée pour l'étude deces composés. La structure locale de film fins de manganite droguéesavec du sodium a été étudiée en fonction de l'épaisseur des film.Des échantillons de poudre de perovskites double droguées avectungstène ont été étudiées pour en caractériser la structure localeen fonction du dopage et pour chercher de comprendre la nature de latransition métal-isolant. Il a été nécessaire de développer undétecteur d'électrons. La réalisation de cet instrument s'est révéléun défi du point de vue technique et il a demandé une quantité detravail aussi bien sur la plan pratique que théorique. Les mesuresd'absorption de rayon-X ont été effectuées à la ligne de lumièreitalienne pour la diffraction et l'absorption (GILDA-BM8) àl'Installation Européenne de Rayonnement de Synchrotron (ESRF) deGrenoble (France)

Reactivities of Fe(II) on Calcite: Selenium Reduction

International audienceThe reductive immobilization of Se(IV) by micrometer-sized (100-200 μm) calcite containing sorbed or coprecipitated Fe(II) was investigated at pH 7 under anoxic conditions (O2 < 1 ppmv) using X-ray absorption near-edge structure (XANES) spectroscopy. The Se(IV) sorption on calcite increased in the presence of sorbed Fe(II) compared to that of Fe-free pure calcite. XANES spectra of Se K-edge shows that nearly half of the total sorbed Se(IV) is reduced to Se(0) by Fe(II) sorbed on calcite within 24 h. The extent of reduction decreases with increasing equilibration time of calcite with Fe(II) solution before Se(IV) addition. The combined results of field emission scanning electron microscopy and X-ray diffraction have shown that needleshaped red monoclinic elemental Se with diameters of 30-50 nm and lengths of up to 100 nm is precipitated on the calcite surface. Fe(II) coprecipitated calcite does not contribute to Se(IV) reduction within 72 h. Therefore, the reduction capacity of Fe(II) linked to calcite critically depends on its location (either on the surface or in the bulk solid), and less extensively on the pre-equilibration time of calcite with Fe(II) solution. Such understanding is important to predict the transport, transformation, and attenuation of Se in subsurface and in nuclear waste repositories

Multi-edge X-ray absorption spectroscopy study of road dust samples from a traffic area of Venice using stoichiometric and environmental references

The appropriate selection of representative pure compounds to be used as reference is a crucial step for successful analysis of X-ray absorption near edge spectroscopy (XANES) data, and it is often not a trivial task. This is particularly true when complex environmental matrices are investigated, being their elemental speciation a priori unknown. In this paper, an investigation on the speciation of Cu, Zn, and Sb based on the use of conventional (stoichiometric compounds) and non-conventional (environmental samples or relevant certified materials) references is explored. This method can be useful in when the effectiveness of XANES analysis is limited because of the difficulty in obtaining a set of references sufficiently representative of the investigated samples. Road dust samples collected along the bridge connecting Venice to the mainland were used to show the potentialities and the limits of this approach

EXAFS, DFT, light-induced nucleobase binding, and cytotoxicity of the photoactive complex cis-[Ru(bpy)2(CO)Cl]+

The aqueous photochemistry of cis-[Ru(bpy)2(CO)Cl]+ (1) was investigated at 310 K and under visible light (white) irradiation by NMR and ESI-HR-MS. Complex 1 releases a Cl ligand, coordinates a solvent molecule, and forms the complex cis-[Ru(bpy)2(CO)(H2O)]2+ (2). Also, irradiation experiments were performed in the presence of the nucleobase derivatives 9-ethylguanine (9-EtG) and 9-ethyladenine (9-EtA). Formation of Ru-9-EtG adducts was observed after 3 h irradiation by NMR and HR-MS, while only very small amounts of a Ru-9-EtA adduct could be detected by HR-MS. Solution structural data were obtained by X-ray absorption spectroscopy (XAS) for both 1 and 2. EXAFS gave a Ru−Cl distance of 2.416(7) Å for 1 and a Ru−OH2O distance of 2.102(6) Å for 2. DFT and TDDFT were employed to study the photophysical and photochemical properties of 1. Calculations show that dissociative metal-centered states can be related to the light-induced release of a Cl ligand and subsequent coordination of a solvent molecule. The compound showed no antiproliferative activity in three human carcinoma cell lines (lung, bladder, pancreas) under the testing conditions, either with or without irradiation with UV light

Acetabular de-escalation in hip revision

Background: The idea of ‘‘de-escalation’’ (DE) indicates an arthroplasty revision performed by changing a revision component by a primary component. Aim of this study is to verify if this technique can represent an option in case of cage or ring failure. Methods: We observed five cases of revision hip cage loosening with complete allograft consolidation. This group of patients were revised with use of a primary cup and were specifically followed in ours institutions offices. Patients were clinically and radiologically followed every 6 months for the next two years and then annually Results: At final follow-up (15-2 years, mean 6 years) four patients (80%) showed a good recovery of their levels of activity. The mean Harris hip score improved from 20 points (range,7-38 points) preoperatively to 48 points (range, 16-88 points). At final radiological follow-up acetabular components were radiographically stable at the last follow-up. One patient (20%) at two years follow-up, was unable to walk without crutchies due to hip pain. X-rays showed cup loosening in all three zones. Patient was dissatisfied. Primary cup was revised with a Burch Schneider cage. Conclusions: De-escalation technique is a surgical option to consider in case of young patients, limited number of previous revisions and more than three years survivorship of loosened acetabular cage. (www.actabiomedica.it)