Oxide

Summary

An oxide (ˈɒksaɪd) is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of –2) of oxygen, an O2– ion with oxygen in the oxidation state of −2. Most of the Earth's crust consists of oxides. Even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a thin skin of (called a passivation layer) that protects the foil from further oxidation. Stoichiometry Oxides are extraordinarily diverse in terms of stoichiometries (the measurable relationship between reactants and chemical equations of an equation or reaction) and in terms of the structures of each stoichiometry. Most elements form oxides of more than one stoichiometry. A well known example is carbon monoxide and carbon dioxide. This applies to binary oxides, that is, compounds containing only oxide and another element. Far more common than binary oxides are oxides o

Official source

https://en.wikipedia.org/wiki/Oxide

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Internal gelation and 3D printing processes were proposed to combine in a process that is promising to produce nuclear fuels with simplified production route and enhanced in-core performance [1]. The process relies on in-situ mixing of feed solutions that bear actinides and uranium nitrates with the methenamine and urea mixture. These feed solutions should be thoroughly mixed and kept at low temperature up to an inkjet printing head, where an inkjet printing process is used to deposit controlled volumes of the mixed solution on the pellet under-fabrication. Microwave and/or laser-heating are then used to trigger the gelation reaction and to solidify these printed dots and later to drive out the excess water and pre-sinter the gelled oxides. The current study is an initial approach to optimize the upfront parameters of the 3D printing process. The feed solutions need be mixed in a passive microfluidic mixer, where the first optimization parameter is the minimum mixing time in the microfluidic mixer that will yield an acceptable mixing level. To do so, CFD modelling using OpenFOAM for different designs of microfluidic mixers was conducted to select the most efficient conception. To validate the CFD results, simulation of microfluidic mixers similar to some literature cases were performed and compared. The uncertainty of selected parameters in the CFD models was used to evaluate a conservative retention time and length. Secondly, the next printing step was modeled with OpenFOAM, which is the droplet generation process. The objective from these models was to correlate the feed parameters like the flow rate and the usage of an acoustic mechanical vibrator to the printed droplets size, generation rate, and the required stand-off distance of the printing head. To perform these CFD simulations with the right solution parameters, rheology and diffusivity measurements were conducted. A proposed empirical approach was investigated for the evaluation of the diffusivity of multi-species solutions. The resultant parameters from the current study are the mixing times and lengths for given microfluidic mixers that are industrially feasible, also, the rate and volume at which the droplets of the broth mixture are generated. These results can be used as guidelines for designing the inkjet printing head and to highlight areas where further investigations are required for an efficient production process.

EPFL2017

Iron-oxides and iron-citrate as new photocatalysts in solar inactivation of Escherichia coli in water

Cristina del Socorro Lonfat

This study addresses the bacterial inactivation mechanism by photo-Fenton process at near-neutral pH, focusing on iron-oxides and iron-citrate as photocatalysts for solar water disinfection and using E. coli as a bacteria model. Cell envelope damage during bacterial inactivation by photo-Fenton and TiO2 photocatalysis were investing providing evidence for lipid peroxidation and cell permeability. TiO2 photocatalysis induced significant cell membrane damage, in contrast to the photo-Fenton process, but the inactivation kinetics for both disinfection processes was similar. A higher efficiency of photo-generation of reactive oxygen species (ROS) in the presence of TiO2 photocatalyst compared with the photo-Fenton system was observed. The bactericidal effect of Fe3+/hv seems possible due to the adsorption of Fe3+ ions on the bacterial cell wall followed by photosensitization of iron-bacteria exciplexes oxidizing the cell membrane. In contrast, the effect of Fe2+/hv was associated with diffusion into the cell giving raise to intracellular dark Fenton¿s reactions. We suggest that cell envelope damage might not necessarily be a unique pathway in bacterial inactivation by photo-Fenton treatment. In particular, the enhancement of an internal (photo)-Fenton process by the synergistic action of UVA and the external Fenton's reactants appears to be an important contribution to bacterial inactivation. Bacterial inactivation by the heterogeneous photo-Fenton process was carried out via iron (hydr)oxide particles, i.e. hematite, goethite, wüstite and magnetite. We found that, the iron (hydr)oxides act as photocatalytic semiconductors and catalysts in the heterogeneous photo-Fenton process with the exception of magnetite, which needs H2O2 as electron acceptors. The Hydroxyl radical and superoxide radical were the principal ROS produced by iron (hydr)oxide particles under light in the absence or presence of H2O2. Natural organic matter (NOM) and inorganic substances did not interfere with the photocatalytic semiconducting action of hematite during bacterial inactivation, but enhanced bacterial inactivation mediated by hematite used as the photo-Fenton reagent. Our results demonstrated, for the first time, that low concentration of iron (hydr)oxides (0.6 mg/L) under sunlight, acting both as semiconductors or catalysts of the heterogeneous photo-Fenton process, may serve as a disinfection method for waterborne bacterial pathogens. Bacterial inactivation by the homogeneous photo-Fenton process was carried out using Fe¿citrate complex as a source of iron. The efficiency of the homogeneous photo-Fenton process using Fe-citrate complex strongly improved bacterial inactivation as compared with the FeSO4 and goethite as sources of iron. The bacterial inactivation rate increased in the order of goethite < FeSO4 < Fe-citrate, which agreed with the ¿OH radicals detected by ESR. Encouraging results were also obtained while applying this treatment for bacterial inactivation in natural water samples at pH 8.5. No bacterial reactivation and/or growth were observed showing that Fe-citrate-based photo-Fenton process efficiently inactivate bacteria using a low iron concentration of Fe-citrate, while avoiding precipitation of ferric hydroxides. The application of the photo-Fenton process at near-neutral pH is a promising technique for bacterial inactivation, due to its simplicity, the use of the sun, the low concentration of reagents and does not produce toxic waste.

EPFL2015

Immobilization of single-walled carbon nanotubes by dielectrophoresis using a microfluidic channel

Paul Louis Mosser

The initial goal of this project was to determine by experimenting on a chip that where already design the ideal parameters for the dielectrophoresis of single walled carbon nanotubes. The epidemic blocking the access to the lab, the subject evolved to focus more on the literature study to compare the different parameters used in the literature for the dielectrophoresis and try to come up with a proposition of parameters to be tested on the chip by someone having access to the laboratory. The dielectrophoresis being the subject of a lot of studies as it is believed to be one of the best solution to build devices with carbon nanotubes, the literature on the subject is huge. It was impossible to take into account all the articles on the subject so this report is based only on the more relevant ones. The motivation behind this project is to find the best parameters possible for the dieletrophoresis in order to immobilized specific nanotubes for specific applications. The first specific application is the immobilization of nanotubes filled with metal-oxide precursors. This could enable the growth of an oxide where the nanotubes are immobilized enabling the fabrication of really small gas sensor based on metal-oxide. The second application presented is the immobilization of DNA functionalized nanotubes which can be used as bioreceptors enabling the detection of specific biomarkers. This could facilitate the fabrication of biosensors. This review show the most important parameters of the dielectrophoresis and how their modification impact the end results. By analyzing the results in the literature and based on the little experimentation made on the platform that was developed for this project, a set of parameters enabling the immobilization of one to a few single walled carbon nanotubes were determined.

2020

EPFL2017

Iron-oxides and iron-citrate as new photocatalysts in solar inactivation of Escherichia coli in water

Cristina del Socorro Lonfat

EPFL2015