Oxyhydroxyde de fer(III)

Résumé

Iron(III) oxide-hydroxide or ferric oxyhydroxide is the chemical compound of iron, oxygen, and hydrogen with formula FeO(OH). The compound is often encountered as one of its hydrates, FeO(OH)·nH2O [rust]. The monohydrate FeO(OH)·H2O is often referred to as iron(III) hydroxide Fe(OH)3, hydrated iron oxide, yellow iron oxide, or Pigment Yellow 42. Anhydrous ferric hydroxide occurs in the nature as the exceedingly rare mineral bernalite, Fe(OH)3·nH2O (n = 0.0–0.25). Iron oxyhydroxides, FeOOH, are much more common and occur naturally as structurally different minerals (polymorphs) denoted by the Greek letters α, β, γ and δ. Goethite, α-FeO(OH), has been used as an ochre pigment since prehistoric times. Akaganeite is the β polymorph, formed by weathering and noted for its presence in some meteorites and the lunar surface. However, recently it has been determined that it must contain some chloride ions to stabilize its structure, so that its more accurate formula is FeO0.833(OH)1.167Cl0.167 or Fe6O5(OH)7Cl. Lepidocrocite, the γ polymorph, is commonly encountered as rust on the inside of steel water pipes and tanks. Feroxyhyte (δ) is formed under the high pressure conditions of sea and ocean floors, being thermodynamically unstable with respect to the α polymorph (goethite) at surface conditions. Siderogel is a naturally occurring colloidal form of iron(III) oxide-hydroxide. Goethite and lepidocrocite, both crystallizing in orthorhombic system, are the most common forms of iron(III) oxyhydroxide and the most important mineral carriers of iron in soils. Iron(III) oxyhydroxide is the main component of other minerals and mineraloids: Limonite is a commonly occurring mixture of mainly goethite, lepidocrocite, quartz and clay minerals. Ferrihydrite is an amorphous or nanocrystalline hydrated mineral, officially FeOOH·1.8H2O but with widely variable hydration. The color of iron(III) oxyhydroxide ranges from yellow through dark-brown to black, depending on the degree of hydration, particle size and shape, and crystal structure.

Source officielle

https://fr.wikipedia.org/wiki/Oxyhydroxyde_de_fer(III)

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Publications associées (1)

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

Concepts associés (5)

Oxyhydroxyde de fer(III)

L’oxyhydroxyde de fer(III), ou oxohydroxyde de fer(III), est un composé chimique de formule FeO(OH) sous forme anhydre. Il s'agit d'un oxyde hydroxyde de fer à l'état d'oxydation +3. Il existe également sous forme hydratée ; le monohydrate peut également être décrit comme l'hydroxyde de fer(III) , et est également appelé oxyde de fer hydraté ou oxyde de fer jaune.

Oxyde de fer

200px|vignette|Poudre d'hématite . La couleur brune rougeâtre indique que le fer est à l'état d'oxydation +III. Un oxyde de fer est un composé chimique résultant de la combinaison d'oxygène et de fer. Les oxydes de fer sont abondants dans la nature, soit dans des roches, notamment minerai de fer, soit dans les sols. Les oxydes de fer, surtout synthétiques, servent soit comme pigments, soit pour leurs propriétés magnétiques.

Minerai de fer

vignette|Rocher formé de minerai de fer rubané, vieux de d'années environ (Musée minéralogique de Dresde). Le minerai de fer est une roche contenant du fer, généralement sous la forme de sulfures, carbonates ou oxydes. L'hématite (oxyde) est le principal minerai utilisé par l'industrie sidérurgique. La teneur en fer des minerais est variable (25 % à 70 %), de sorte que la teneur du minerai est un critère souvent plus important que sa distance géographique d'un point de vue économique.

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

Cristina del Socorro Lonfat

EPFL2015