Electron sources for plasma electronics and different technological application

There are the following advantages of applying electron guns with plasma cathodes in devices exciting microwave radiation: stability of their parameters, high density of current, relative insensitivity to ion bombardment and the possibility of operating over a wide range of pressure values of a plasma-generating gas [1-5]. The given work aims at constructing the guns with the parameters necessary for the excitation of microwaves of high amplitudes in the slow-wave structures: the beam energy is 20-30 kV, the current is up to 5 A, and the pulse duration is 0,11÷1 ms. The principal problem arising during construction of heavy-current electron sources with plasma emitters consists in the following: it is necessary to provide such conditions of the gas volume, under which the discharge firing would be stable and the emissive plasma generation be effective, whereas a gas breakdown in the accelerating gap must be eliminated

Biogenèse d'hydroxysels mixtes Fe(II-III) de type rouille verte en culture de Shewanella putrefaciens

Les rouilles vertes sont des oxydes de fer à valence mixte Fe(II-III) dont l'existence formelle dans l'environnement naturel, bien que suspectée depuis longtemps, n'a été mise en évidence que depuis quelques années. Considérés comme étant au coeur des phénomènes de corrosion aqueuse du fer et des réactions d'oxydoréduction des espèces du fer dans les milieux anaérobies, ajouté au fait qu'ils présentent une forte réactivité vis-à-vis de nombreux polluants, l'étude de tels composés présente un intérêt majeur. Les mécanismes de formation des rouilles vertes dans l'environnement restent inconnus. Les microorganismes sont fortement suspectés d'être à l' origine de l' occurrence de ce minéral. Pour le montrer, nous avons cherché à produire des rouilles vertes au cours d'une culture microbienne et à mettre en évidence le rôle de certains paramètres physiques, chimiques et biologiques sur la formation de ces minéraux. Shewanella putrefaciens a été choisie comme modèle microbien afin de produire des rouilles vertes. Cette bactérie a l'avantage d'être facile à cultiver et fait partie des microorganismes rencontrés dans les environnements réducteurs tout en ayant la capacité à réduire les formes solides du Fe(III) (FeOOH et Fe2O3). La nature des phases présentes dans les cultures bactériennes a été identifiée sans ambiguïté à l'aide de méthodes d'investigation du solide comme la diffraction par rayons X, la spectroscopie infrarouge par réflexion diffuse ou la spectrométrie Mossbauer. Ainsi, les rouilles vertes carbonatée ou sulfatée ont été obtenues au cours de la réduction bactérienne de la lépidocrocite y-FeOOH dans des conditions définies. Jusqu'à 90% du fer présent peut ainsi se trouver sous forme de rouille verte. Le rapport Fe(II)/Fe(III) varie de 1 à 2 pour la rouille verte carbonatée, la formule générale attribuée à cette rouille verte s'écrit alors : [FeII(1-x)FeIIIx(OH)2]x+ .[(x/2)CO32-yH2O]x-, avec y >= [1-(3/2)x]. Selon l'activité microbienne, l'oxyhydroxyde ferrique de départ peut donner lieu soit à de la rouille verte, soit à de la magnétite. En particulier, les concentrations relatives en accepteur d'électrons (Iépidocrocite) et la cinétique de production de Fe(II) sont les facteurs essentiels qui gouvernent ces formations. La nature des espèces en solution et celle de l' oxyde ferrique de départ sont également des paramètres qui conditionnent la nature du minéral obtenu. En conclusion, ce travail permet de confirmer que l'activité microbienne ferriréductrice conduit à la formation de rouilles vertes sulfatée ou carbonatée à partir de formes cristallisées du Fe(III). Les microorganismes contribuent donc bien à la présence de ces minéraux dans les environnements anoxiques. Par ailleurs, l' activité biologique peut affecter directement la nature des minéraux ferreux-ferriques en modulant la cinétique de production de Fe(II).NANCY1-SCD Pharmacie-Odontologie (543952101) / SudocSudocFranceF

Environmental, Biomedical, and Industrial Applications of Biogenic Magnetite Nanoparticles

Magnetite is the most abundant magnetic iron mineral on the Earth’s surface. Its formation in natural ecosystems is mainly due to microbial activity. Microbially synthesized magnetite, commonly called “biogenic magnetite,” has many beneficial properties for a wide range of environmental and commercial applications. Its high surface reactivity facilitates interactions with (in)organic pollutants in anthropic and natural ecosystems, as well as with reagents in industrial catalysis. Due to its magnetic properties and good biocompatibility, biogenic magnetite is also well suited for biomedical applications such as cancer treatment or drug delivery. Biomineralization of magnetite offers an inexpensive and sustainable method for the production of this highly functional material. Moreover, this biomineralization process results in a biomolecule coating of the magnetite, making it highly amenable to further functionalization. This chapter reviews the application of biogenic magnetite across environmental, medical, and industrial settings. Existing challenges and future opportunities in these applications are also discussed.</p

Hydroxy-nitrite green rust: a new type of green rust formed as an intermediate reaction product

International audienceThe presence of high nitrite concentrations due to anthropogenic activities is an important water quality concern as nitrite is highly toxic to human and fauna. Nitrite toxicity is related to its transformation into carcinogenic N-nitroso compounds that are suspected to be responsible for some gastric cancers, and to its ability to convert the hemoglobin to methaemoglobin what is then unable to fix oxygen and to transport it to the tissues, resulting in hypoxia and the blue-baby syndrome [1]. To reduce the adverse effect of nitrite on human health, any process enhancing the transformation of nitrite ions to nitrogen gas is of interest for the remediation processes. This purpose can be achieved by using green rusts (GR) that are mixed iron(II-III) layered double hydroxides, commonly found in anoxic zones of natural environments. They play an important role in the geochemical redox cycling of iron and nitrogen, and can affect the speciation and mobility of many (in)organic contaminants. Here we investigate nitrite reduction by biogenic iron(II-III) hydroxycarbonate green rusts under anoxic conditions. Results reveal that biogenic GR are capable of reducing nitrite ions without ammonium production, suggesting the conversion of nitrite to nitrogen gaseous species. Moreover, the study provides evidence for the first time of the formation of a hydroxy-nitrite green rust as an intermediate reaction product prior to the fully oxidation of GR to ferric oxyhydroxides

Oxidative transformation in the environment of a quinolone sorbed on nano-magnetite via Fe2+/O2 mediated reactions

Oxidative transformation in the environment of a quinolone sorbed on nano-magnetite via Fe2+/O2 mediated reactions. 1st International Conference on Risk Assessment of Pharmaceuticals in the Environment - ICRAPH

Constraining the origins of the magnetism of lepidocrocite (γ-FeOOH): a Mössbauer and magnetisation study

International audienceLepidocrocite, a widespread environmentally relevant iron oxyhydroxide, has been investigated for decades using 57Fe Mössbauer spectroscopy and magnetic measurements. However, a coherent and comprehensive interpretation of all the data is still lacking due to seemingly contradictory interpretations. On one hand, temperature dependence of magnetic susceptibility and Mössbauer spectra resemble those of superparamagnetic nanoparticles with diameters less than 10 nm even though physically particles are lath-shaped with lengths on the order of 100-300 nm. On the other hand, in-field Mössbauer spectra show that lepidocrocite is an antiferromagnet and becomes paramagnetic above 50-70 K, a temperature close to the blocking temperature deduced from susceptibility data. The present study investigates a well-characterized synthetic sample of lepidocrocite, includes modelling of Mössbauer spectra and dc and ac magnetization data, and proposes a solution to this paradox. The new data are coherent with the presence of two entities in lepidocrocite: a bulk antiferromagnetic matrix and sparse ferrimagnetic nanosized inclusions (d = 3.4 nm), akin to maghemite, embedded within. The presence of nanosized ferrimagnetic inclusions is confirmed for the first time by Mössbauer spectroscopy

Dissolved metal ions and mineral-liposome hybrid systems: Underlying interactions, synthesis, and characterization

International audienceLiposomes are versatile lipid-based vesicles with interesting physicochemical properties, making them excellent candidates for interdisciplinary applications in the medicinal, biological, and environmental sciences. The synthesis of mineral-liposome hybrid systems lends normally inert vesicles with the catalytic, magnetic, electrical, and optical properties of the integrated mineral species. Such applications require an understanding of the physicochemical interactions between organic molecules and inorganic crystal structures. This review provides an overview on these interactions and details on synthesis and characterization methods for these systems

Absence of solid solution between Fe(II) and Mg(II) hydroxides and consequences on formation of fougerite and smectites

International audienceAs there exists extended solid solutions between ferrous and magnesian silicates, experiments were conducted to check if ferrous and magnesian hydroxides can co-precipitate in a solid solution. Results show that no solid solution forms and instead Fe(II) and Mg(II) hydroxides precipitate separately with the same solubilities as pure components. However, in fougerite, F(III), Fe(II) and Mg(II) coexist in a brucitic type hydroxide, with an extended solid solution. This implies that fougerite formation results from Fe(III) precipitation, Fe(III) being surrounded by divalent Fe(II) and Mg(II) to comply with the exclusion rule: Fe(III) ions cannot be direct neighbours. Consequently, Fe(III)-Fe(II)-Mg(II) smectites cannot form by oxidation of a ferrous-magnesian brucitic layer, but by silication of fougerite. The impossibility of formation of a solid solution between Fe(II) hydroxide and Mg(II) hydroxide, while their electric charge and ionic radii are identical can be explained by the differences of electronegativities of the elements. Fe(II) and Mg(II) can dimerize separately in aqueous solution, but an heterodimer cannot form

Oxidative removal of organic contaminants via Fe-oxide/O2-mediated reactions

Organic pollution has become a critical issue worldwide due to the increasing input and persistence ofsome organic compounds in the environment. Various minerals, which are ubiquitous in natural waters,sediments and soils, are potentially able to adsorb organic pollutants on their surfaces and to degradethem via oxidative or reductive transformation processes [1]. Recently, increasing attention has beenpaid to heterogeneous Fenton-like reactions using iron-bearing minerals as catalyst [2]. Iron oxideshave attracted attention because of their nanometric-size particles, large surface area, high sorptionability and stability. The modified Fenton process can efficiently oxidize pollutants at different pHvalues mainly by the generation of reactive oxygen species and allows avoiding some disadvantages ofthe classic Fenton reaction such as the preliminary acidification and the formation of sludge. However,most of previous studies were focused on the use of strong oxidants [3] and only few of them consideredthe role of oxygen in the oxidative degradation [4]. In the present study, we explored the oxidative capacity of iron oxides nanoparticles, as catalyst for heterogeneous Fenton-like reactions mediated by oxygen, in the removal of a recalcitrant quinolone antibacterial agent. Results showed an efficient sorption under anoxic conditions, followed by a rapid removal of the model contaminant when exposed to air, while negligible degradation is observed in the absence of oxygen or of iron oxides. Four by-products issuing from the oxidative degradation of the antibacterial agent were observed by liquid chromatography-mass spectrometry. Mass balance analyses however indicate that most of the initial contaminant may have been fully degraded. X-ray powder diffraction and Fe K-edge X-ray absorption spectroscopy were used to investigate mineralogical andiron redox changes upon oxidative degradation of the contaminant. Results indicate a significant andsystematic oxidation of the solid phase in the oxic experiments, which suggests that the iron oxide enhances the degradation of the contaminant. This study points out the promising potentialities of iron oxides for the treatment of soils and wastewater contaminated by organic pollutant