Structural study of Pb(II) and Sb(V) adsorption on the hydroxylated hematite(1102) surface

Thesis (Ph.D.) University of Alaska Fairbanks, 2015Surface complexation reactions at mineral-water interface play a key role in dictating the mobility and bioavailability of aqueous species in the environment, considering the minerals (like iron-(oxyhydr)oxides), ubiquitous in nature, are usually of high specific surface area and contain a lot of potentially reactive surface sites for binding ions. Thus, the fundamental understanding of surface complexation reactions is essential to better model the environmental fate and transport of toxic aqueous species. In the current study, the hematite (1102) surface was selected as a model substrate for iron-(oxyhydr)oxides commonly found in the environment to investigate the surface complexation reactions of Pb(II) and Sb(V) using the crystal truncation rod (CTR) surface diffraction. The hematite (1102) surface displays two surface terminations, the half layer termination (HLT) and the full layer termination (FLT) depending on sample preparation schemes. Previous CTR studies of clean hydrated hematite (1102) surface indicated that the chemically mechanical polishing procedure favors a HLT surface, while an annealing procedure favors the FLT surface. Our CTR results on the clean annealed hematite (1102) surface provides structural evidence that the substrate annealed in air undergoes a surface termination transformation that occurs through the projection of the near surface Fe atoms from original lattice sites to occupy top vacant Fe sites. The adsorption of Pb(II) on the hydrated hematite(1102) surface was also studied using CTR diffraction. Our findings demonstrate that aqueous Pb(II) adsorbs at two types of bidentate edgesharing sites on the HLT surface, whereas the surface adsorption of Pb(II) occurs only at one type of edge-sharing site on the FLT surface. The site preference could be rationalized through comparing O-Fe-O bond angles for different edge-sharing binding sites. It was found that Pb binding at edge-sharing sites with relatively large O-Fe-O bond angles (>100°) is unfavorable as a result of forming a Pb complex species with extremely long (weak) Pb-O bonds (>2.5Å). On the contrary, an edge-sharing site with relatively small O-Fe-O bond angles would be more favorable for binding Pb(II) species, since it would give rise to a surface complex species with reasonable Pb-O bond lengths (~2.25Å). Differing from the case of Pb(II), the Sb(V) adsorption on the hematite (1102) surface with the HLT occurs only at a tridentate site in a binuclear edge-sharing/corner-sharing binding mode. The bidentate binding configurations are apparently not favorable due to the steric constraints caused by the Sb-bonded hydroxyl groups, which are abnormally close to the surface oxygen groups. The molecular scale structural details presented in this study improve the understanding of the surface adsorption of Pb(II) and Sb(V) on the hematite(1102) surface. Our findings also give evidence that the surface reactivity is largely determined by the surface structure through steric constraints as a function of sorbate type

Ultra trace analysis of 17 organochlorine pesticides in water samples from the Arctic based on the combination of solid-phase extraction and headspace solid-phase microextraction-gas chromatography-electron-capture detector

Solid-phase extraction (SPE) was combined with headspace solid-phase microextraction (HS-SPME) for the highly effective enrichment of 17 ultra trace organochlorme pesticides in water samples The [at-get compounds were successfully transferred from water samples to a gas chromatography capillary column by means of four consecutive steps, namely SPE, solvent conversion. I IS-SPME, and thermal desorption of the SPME fiber Parameters. including elution volume and breakthrough volume in the SPE step, temperature in the solvent conversion step. and fiber type. ionic strength, extraction temperature e. extraction time, and phi in the SPME step were optimized to Improve the pet of the method through either single factor comparative experiment or the orthogonal experimental design approach After optimization. the method gave high sensitivity with a method detection limit ranging from 0 0018 to 0027 ng L-1. good repeatability with a relative standard deviation less than 20% (IT =4) and acceptable recovery with a value mostly exceeding 60% External standard calibration was employed for the quantification, and a wide linear range (from 00010 to 60ng mL(-1)) with R-2 values ranging from 09988 to 09999 were observed In the end. the method was successfully applied to the Arctic samples. and the results showed that, among all the organochlorine pesticides, hexachlorocyclohexanes (HCHs) were the most predominant in the Arctic SLIT face water body with SLIM of their concentrations ranging from 0 262 to 3 156 ng L-1 (C) 2009 Elsevier B V All rights reserve

Instrumentation du transshipment d'urgence comme mode de coopération pour l'amélioration du pilotage des flux dans les réseaux de distribution

Le transshipment (latéral) d urgence au sein des réseaux de distribution consiste à organiser les transferts de stocks entre les détaillants pour faire face aux situations de rupture. Sa mise en œuvre amène à arrêter une stratégie appropriée et à harmoniser ses paramètres avec la politique et paramètres de gestion des stocks, dans l objectif de garantir un taux de satisfaction des demandes clients au moindre coût. Le présent travail se situe dans ce contexte et s est focalisé sur l analyse des apports de la mise en œuvre du transshipment d urgence dans un système de pilotage de flux tirés par des demandes clients probabilistes, avec des politiques locales de gestion de stock du type (R, s, S). Notre étude a porté sur trois structures différentes de réseau : système de stock à deux échelons et à deux détaillants, avec coût unitaire de transshipment ; système de stock à deux échelons et à détaillants multiples, avec coût fixe de transshipment ; système de stock multi échelons à deux détaillants, avec coût fixe de transshipment. Pour chacune de ces structures, nous avons analysé le comportement du système pour différentes combinaisons des paramètres d entrée (délais d approvisionnement, écarts types de la demande et nombre des détaillants) et des paramètres de coût (commande, possession, rupture et transshipment). Nous avons visé à déterminer, sur un horizon fini de périodes, les seuils de stocks (s et S chez les détaillants et chez le centre de distribution) qui minimisent le coût total du système tout en garantissant un taux de service désiré. Dans ce cadre, quatre politiques de transshipment ( tout ou rien , complete pooling standard , complete pooling plafonné et complete pooling conditionné ) ont été explorées. L étude est d abord ébauchée selon une approche analytique puis approfondie par l élaboration et l expérimentation de modèles dont la résolution est basée sur la simulation-optimisationThe lateral emergency transshipment in distribution systems consists in organizing inventory transferts between retailers to face shortage situations. Its implementation leads to adopt an appropriate transhipment policy and harmonize its parameters with inventory policy parameters and inventory control policy. The objective is to ensure a desired service level at minimum cost. Thie work is situated in this context and focused on the analysis of emergency transhipment benefits in distribution systems faced to random customers demand. Each retailer used an (R,s,S) inventory control policy. Our study is related to three different distribution systems structure : two echelons two retailers inventory system with unit transhipment cost; two echelons multi retailers inventory system with fixed transhipment cost; multi echelons multi retailers inventory system with fixe transhipment cost. For each of these structures we analyzed the sensibility of system behaviour to input parameters. Our objective is to determine on a finite horizon the inventory parameters (s, S) that minimize total cost under service level condition.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocVILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

Atomic-scale surface restructuring of copper electrodes under CO2_2 electroreduction conditions

Potentiodynamic methods that induce structural changes in Cu catalysts for the electrochemical reduction of CO$_2$ (CO2RR) have been identified as a promising strategy for steering the catalyst selectivity towards the generation of multi-carbon products. In current approaches, active species are created via a sequential Cu oxidation–reduction process. Here we show by in situ scanning tunnelling microscopy, surface X-ray diffraction and Raman spectroscopy measurements that low-coordinated Cu surface species form spontaneously near the onset of CO$_2$ electrocatalytic reduction. This process starts by CO-induced Cu nanocluster formation in the initial stages of the reaction, leading to irreversible surface restructuring that persists over a wide potential range. On subsequent potential increase, the nanoclusters disperse into Cu adatoms, which stabilize reaction intermediates on the surface. The observed self-induced formation of undercoordinated sites on the CO$_2$-converting Cu catalyst surface can account for its reactivity and may be exploited to (re)generate active CO$_2$RR sites by potentiodynamic protocols

Concentration and distribution of 17 organochlorine pesticides (OCPs) in seawater from the Japan Sea northward to the Arctic Ocean

Seventeen classic organochlorine pesticides in surface seawater were studied in terms of their composition pattern as well as their distribution pattern in the areas covering the Japan Sea, Okhotsk Sea, Bering Sea, Chukchi Sea and Arctic Ocean. Their concentrations varied, but roughly two levels were seen with one ranging between 0.1 and 1 ng L-1 for most HCH isomers and the other lower than 0.1 ng L-1 for other chemicals. Of the 17 target compounds, HCHs were dominant with a total concentration percentage generally more than 50%, and a relatively high concentration percentage of heptachlor and aldrine was also observed at scattered stations. The historical long-term trend of several target chemicals in the five sea zones considered was discussed in comparison with previous reports. Inter-sea zone comparison was carried out for individual chemicals by comparing the concentration variation in all five sea zones. A higher variation in concentration was generally found in the northern sea zones, namely the Bering Sea, Chukchi Sea and Arctic Ocean, for most target compounds. The sum concentration of the 17 target chemicals displayed a general trend of increasing northward from the Japan Sea to the Okhotsk Sea to the Bering Sea to the Arctic Ocean. Different latitudinal trends were found for alpha-HCH and gamma-HCH, and the reason of this difference was discussed by considering their divergence of thermodynamic properties, which could contribute to a slightly different fractionation effect during their northward transport driven by atmospheric long range transport. The source of the HCHs was identified by analyzing the alpha-HCH/gamma-HCH ratio, which was less than 4 without exception, indicating a component characteristic featuring a mixture of technical HCHs and lindane. In addition, the vertical distribution of alpha-HCH, gamma-HCH and their ratio at station B80 was discussed. Different patterns were found in the upper 300 m while in layers from 300 m downward to 3500 m the patterns were fairly comparable. The vertical profiles were used to correlate the water mass distribution, based on which four layers were tentatively classified at station B80.National Natural Science Foundation of China [40776040, 40306012, 40776003]; National High Technology Research and Development Program of China [2007AA09Z121]; Ocean Public Welfare Scientific Research Project ; State Oceanic Administration of China [200805095]; Fujian Provincial Department of Science Technology [2005Y021]; Chinese Arctic and Antarctic Administration, State Oceanic Administration of Chin

Heavy metals in surface sediments from mangrove zone in Zhangjiang River estuary, South China

Conference Name:International Conference on Environmental Science and Information Application Technology (ESIAT 2009). Conference Address: Wuhan, PEOPLES R CHINA. Time:JUL 04-05, 2009.Concentrations of selected heavy metals (Cr, Cu, Zn, As, Cd, Hg and Ph) in surface sediments from 18 sites were examined in Zhangjiang Estuary Mangrove National Natural Reserve (ZEMNNR), which is the largest natural mangrove forest at the north of tropic of Cancer in China. The ranges of heavy metals expressed in mu g/g sediment dry weight were as following: Cr (48.14 to 110.01), Cu (18.15 to 43.18), Zn (119.53 to 136.13), As (12.05 to 16.16), Cd (0.25 to 0.58), Hg (ND to 0.10) and Ph (55.61 to 67.71). Slight distribution changes implicate inflow from Zhangjiang River offered most Zn, As, Cd, Hg and Ph; While for Cr and Cu, anthropogenic activities might he another important source. The levels of Ph exceed sediment quality criteria ( I Class) and may show a potential risk to ecosystems. The values of 1,,,, indicate that Zhangjiang estuary mangrove zone is moderately polluted by Ph and slightly polluted by Cd, As and Cr

Operando Identification of the Reversible Skin Layer on Co3O4 as a Three-Dimensional Reaction Zone for Oxygen Evolution

International audienceCo oxides and oxyhydroxides have been studied extensively in the past as promising electrocatalysts for the oxygen evolution reaction (OER) in neutral to alkaline media. Earlier studies showed the formation of an ultrathin CoOx(OH)(y) skin layer on Co3O4 at potentials above 1.15 V vs reversible hydrogen electrode (RHE), but the precise influence of this skin layer on the OER reactivity is still under debate. We present here a systematic study of epitaxial spinel-type Co3O4 films with defined (111) orientation, prepared on different substrates by electrodeposition or physical vapor deposition. The OER overpotential of these samples may vary up to 120 mV, corresponding to two orders of magnitude differences in current density, which cannot be accounted for by differences in the electrochemically active surface area. We demonstrate by a careful analysis of operando surface X-ray diffraction measurements that these differences are clearly correlated with the average thickness of the skin layer. The OER reactivity increases with the amount of formed skin layer, indicating that the entire three-dimensional skin layer is an OER-active interphase. Furthermore, a scaling relationship between the reaction centers in the skin layer and the OER activity is established. It suggests that two lattice sites are involved in the OER mechanism

ROBL‐II at ESRF: a synchrotron toolbox for actinide research

ROBL‐II provides four different experimental stations to investigate actinide and other alpha‐ and beta‐emitting radionuclides at the new EBS storage ring of ESRF within an energy range of 3 to 35 keV. The XAFS station consists of a highly automatized, high sample throughput installation in a glovebox, to measure EXAFS and conventional XANES of samples routinely at temperatures down to 10 K, and with a detection limit in the sub‐p.p.m. range. The XES station with its five bent‐crystal analyzer, Johann‐type setup with Rowland circles of 1.0 and 0.5 m radii provides high‐energy resolution fluorescence detection (HERFD) for XANES, XES, and RIXS measurements, covering both actinide L and M edges together with other elements accessible in the 3 to 20 keV energy range. The six‐circle heavy duty goniometer of XRD‐1 is equipped for both high‐resolution powder diffraction as well as surface‐sensitive CTR and RAXR techniques. Single crystal diffraction, powder diffraction with high temporal resolution, as well as X‐ray tomography experiments can be performed at a Pilatus 2M detector stage (XRD‐2). Elaborate radioprotection features enable a safe and easy exchange of samples between the four different stations to allow the combination of several methods for an unprecedented level of information on radioactive samples for both fundamental and applied actinide and environmental research.ROBL‐II at ESRF provides four experimental stations to investigate actinides with X‐ray absorption and emission spectroscopy, and with surface, high‐resolution powder, and single‐crystal X‐ray diffractometry