Sulfate reduction processes in salt marshes affected by phosphogypsum: Geochemical influences on contaminant mobility

Sulfate reduction and its associated contaminant immobilization in marsh soils supporting a phosphogypsum stack was examined by pore-water and solid analysis, selective extractions, microscopy and sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The negative impact of this stack on estuarine environments is a concerning problem. In the weathering profile, total concentrations of most pollutants increase with depth; instead, dissolved contents in pore-waters increase to middle of the saturated zone but then decrease drastically down to reach the marsh due to sulfide precipitation. Excess of acid-volatile sulfide plus pyritic sulfur over metals bound to the oxidizable fraction indicates that sulfide precipitation is the main mechanism responsible for metal removal in the marsh. Thus, abundant pyrite occurred as framboidal grains, in addition to other minor sulfides of As, Zn and Cu as isolated particles. Moreover, high contents of elemental sulfur were found, which suggest partial sulfide oxidation, but marsh may have capacity to buffer potential release of contaminants. The importance of sulfur species was quantitatively confirmed by XANES, which also supports the accuracy of selective extraction schemes. Accordingly, managing pore-water quality through organic carbon-rich amendments over phosphogypsum stacks could lead to a decrease in contaminant loading of leakages resulting from weathering.

Manipulating the morphology of the nano oxide domain in AuCu–iron oxide dumbbell-like nanocomposites as a tool to modify magnetic properties

We highlighted the effects of oleic acid on the structural and magnetic properties of colloidal nanodumbbells.

Determination of the S-ZnO structural interaction in thiol-capped ZnO nanoparticles: a sulfur K-edge XAS study

ZnO nanoparticles capped with thiol molecules display room temperature ferromagnetism which has been associated with the structural details of the interface formed between the organic molecule and the ZnO core. Although the local order around sulfur atoms at the ZnS/ZnO interface has been related to the occurrence of the ferromagnetic like behavior, no direct structural determination has been obtained yet. We report here a detailed x-ray absorption spectroscopy study performed at the sulfur K-edge to determine the local structure around the sulfur atoms in these systems and how it is modified by varying the length of the organic molecule.

Detection of vancancies by using XAS, is it possible? The case of ZnO

The occurrence of high temperature ferromagnetism (HTFM) in transition-metal-doped ZnO systems has attracted much attention in the last years. In particular, the Mn–Zn–O system has been widely studied and large efforts have been aimed at finding Curie temperatures above room temperature (RT). However the origin of that magnetic behaviour has not been explained yet. While doubts rise about the role of the 3d cations, several types of defects, such as oxygen and zinc vacancies, as well as hydrogen, oxygen and zinc interstitials, have been proposed by different authors to induce HTFM [1]. Aiming at determine the exact type of defect that causes the HTFM in these systems several experimental tools, such as x-ray absorption spectroscopy, have been applied. However, based on similar experimental spectra, different authors report opposing conclusions regarding the nature of defects involved in the observed HTFM [2,3]. These results pose serious doubts about the real capability of XAS to determine the presence of vacancies in these systems and, consequently, to shed light on the origin of the magnetism in these systems. Here we report a XANES study at both Mn and Zn K-edges in Zn(0.95)Mn(0.05)O thin films prepared with different sputtering gases (pure Ar, Ar/N2 and Ar/O2). We have studied the local order around Mn in the films, by means of ab initio XANES calculations. During this study, a special emphasis has been paid to determine the role played by both vacancies and structural distortions associated with the substitution of Zn by Mn in the ZnO host. Our results indicate that XANES is not sensitive to the presence of randomly distributed vacancies. On the contrary, the observed modifications of the XANES spectra are associated with the structural distortion around Mn sites, which rules the magnetic behaviour of these Mn:ZnO thin films in terms of the different sputtering gases involved in the preparation.

X-ray absorption study of the local order around Mn in Mn:ZnO thin films: the role of vacancies and structural distortions

This work reports an x-ray absorption near-edge structure spectroscopy (XANES) study at both Mn and Zn K edges in Zn(0.95)Mn(0.05)O thin films prepared with different sputtering gases (pure Ar, Ar/N(2) and Ar/O(2)). We have studied the local order around Mn in the films, with special emphasis on the role played by both oxygen and zinc vacancies and by the structural distortion associated with the substitution of Zn by Mn in the ZnO host. Our results indicate that the dependence of the magnetic properties of these Mn:ZnO thin films on the different sputtering gases used in the preparation is related to the structural distortion around Mn sites.

Cocket syndrome: thrombotic-septic disease post-appendicectomy complication

The incidence of complications following treatment of acute appendicitis in childhood is lower than 5%, while thromboembolic disease at that age is exceptional. The case of a 13-year-old male who was operated on in our pediatric surgery department for acute gangrenous appendicitis is presented. His condition improved until the sixth day after the operation when he suffered thrombosis in both the left iliac vein and the inferior cava. Ultrasonography, plethysmography and computer tomography (CT) studies were carried out and a diagnosis of venous thrombosis was made with an underlying congenital vascular malformation where the iliac vein was compressed by the overlying iliac artery; known as the Cocket syndrome. The etiology diagnosis and treatment of this rare disease in childhood is reviewed.