Ferrites de cobalt nanostructurés ; élaboration, caractérisation, propriétés catalytiques, électriques et magnétiques

Ce travail est consacré à l élaboration et l étude des propriétés catalytiques, électriques et magnétiques denanomatériaux à base de ferrite de cobalt. Les nanopoudres de ferrite de cobalt (CoxFe3-xO4 , x=0.6,1,1.2,1.8 ) ont étéélaborées par une nouvelle méthode chimique solvo-thermale. Les nanopoudres obtenues sont très bien cristallisées ontdes tailles de particules qui varient avec le taux de cobalt entre 4 et 7 nm et sont très homogènes en composition. Lesnanopoudres de ferrites de cobalt sont monophasées, de structure spinelle avec un paramètre de maille qui varie enfonction du taux de cobalt. Les nanopoudres de ferrites de cobalt ne s oxydent pas sous air et en température .Lesnanopoudres de composition proches de x=1 sont stables jusqu à 900C, alors que pour de plus forts écarts à lastoechiométrie, des transformations de phase ont lieu au delà de 550C.Les mesures catalytiques ont mis en évidence l oxydation de CH4 en CO2 après passage sur le catalyseur pour tous leséchantillons. L efficacité catalytique est maximale et l énergie d activation est la plus faible pour l échantillon x=1.8 ;ceci est lié à la plus grande surface spécifique, et au plus fort taux de sites actifs pour cette composition.Les ferrites de cobalt élaborées présentent une conduction de type électronique avec un comportement semi conducteurjusqu à 500-600C et un comportement métallique au-delà. Les variations de conductivité d une composition à l autres expliquent par les variations du nombre de paires [Co2+,Fe3+].Les nanoparticules ont un comportement superparamagnétique quelle que soit la composition. Ce comportement estdû principalement à un effet de taille et de forme, et à une distribution cationique différente entre les deux types desites tétraédriques et octaédriques de la structure spinelle. Ces ferrites présentent une aimantation à saturation prochede celle de l état massif, du fait de la grande qualité cristalline attribuée à la méthode d élaboration mise au point.This work is devoted to the synthesis and the study of the physical properties of cobalt ferrite nanomaterials. Thecobalt ferrite nanopowders (CoxFe3-xO4 , x=0.6,1,1.2,1.8 ) were synthesized by a new solvo thermal chemical route.The nanopowders are highly crystallized, very homogeneous in size and chemical composition. The nanopowderssizes are ranged from 4 nm for high cobalt content to 7 nm for low cobalt content. They are single phased, with thespinel structure, and a cell parameter varying with the cobalt content. The cobalt ferrites do not oxidize, when heatedunder air. For compositions near x=1, the cobalt ferrites are stable when heated under air up to 900C, as for the othercompositions, phase transformations occur above 550C.The catalytic measurements have shown the oxidation of CH4 into CO2 in presence of the catalyst for all thecompositions. Cobalt ferrite with composition x=1.8, presents the lowest activation energy and the best catalyticefficiency; this can be related to the great specific surface and the high rate of active sites for this composition.Concerning the conduction properties, the cobalt ferrites exhibit a semiconductor character up to 500-600 C and ametallic one above. Changes in conductivity from a composition to another are explained by changes in the number ofpairs [Co2+, Fe3+].A superparamagnetic behaviour was evidenced whatever the composition. This is due for one part to a size and shapeeffect and for the other part to different cationic distribution between tetrahedral and octahedral sites. These ferriteshave a saturation magnetization close to that of the massive state, because of the high crystallinity of the nanopowders,attributed to the synthesis method developed in this work.TOULON-Bibliotheque electronique (830629901) / SudocSudocFranceF

Magnetic, electric and thermal properties of cobalt ferrite nanoparticles

International audienceThe electric and magnetic properties as well as the thermal stability of CoxFe3-xO4 nanopowders, (0.

Assessment of renal safety of tenofovir disoproxil fumarate in people living with HIV in Tunisia

Background: Tenofovir disoproxil fumarate (TDF) is a nucleotide reverse transcriptase inhibitor (NRTI). TDF is generally well tolerated. It is eliminated by the combination of glomerular filtration and active renal tubular secretion. Thus, it can be responsible, in the medium and long term, of renal toxicity. The aim of our study is to assess the prevalence of TDF nephrotoxicity and its factors risk in PLHIV treated in the Infectious Diseases Department at the University Hospital of Monastir, Tunisia.. Methods: An observational cross-sectional single-centre prospective study included 62 cases of HIV-infected patients taking antiretroviral therapy (ART) containing TDF was conducted between 1st August 2016 and 31 December 2016 at Fattouma Bourguiba University Hospital of Monastir, in Tunisia. During this period, patients were screened for renal dysfunction to detect renal toxicity, Tubular dysfunction or Fanconi syndrome. Results: 62 patients were included with female/male ratio at 1,52. The mean age was 39 years ± 8,5 years. Half of the patients were treated with TDF as first-line therapy. The average duration of TDF was 25 months, the duration was greater than 12 months in 40 (65%) patients. There was a decrease in creatinine clearance in 21 (33.8%) patients, the average of the decrease was 128,6 ±35,8 ml/min Proximal tubulopathy was noted in 1 patient (1.6%) and no patient had Fanconi syndrome.  No risk factors for renal impairment under TDF were found. This finding could be explained by the small sample size Conclusion: TDF-related renal toxicity is often asymptomatic, it require early detection. In ours patient cases, TD is rare, but creatinine clearance decrease is frequent and may inform of possible TD in these patient. In order to reduce TDFtoxicity, a new pro-drug, tenofovir alafenamide (TAF), is now available

Etude des degradations dans les diodes electroluminescentes n GaAlAs/p GaAlAs par spectroscopie de photoluminescence

Available from INIST (FR), Document Supply Service, under shelf-number : TD 83521 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Nanostructured cobalt ferrite; elaboration, characterization, catalytic, electric and magnetic properties

Ce travail est consacré à l’élaboration et l’étude des propriétés catalytiques, électriques et magnétiques denanomatériaux à base de ferrite de cobalt. Les nanopoudres de ferrite de cobalt (CoxFe3-xO4 , x=0.6,1,1.2,1.8 ) ont étéélaborées par une nouvelle méthode chimique solvo-thermale. Les nanopoudres obtenues sont très bien cristallisées ontdes tailles de particules qui varient avec le taux de cobalt entre 4 et 7 nm et sont très homogènes en composition. Lesnanopoudres de ferrites de cobalt sont monophasées, de structure spinelle avec un paramètre de maille qui varie enfonction du taux de cobalt. Les nanopoudres de ferrites de cobalt ne s’oxydent pas sous air et en température .Lesnanopoudres de composition proches de x=1 sont stables jusqu’à 900°C, alors que pour de plus forts écarts à lastoechiométrie, des transformations de phase ont lieu au delà de 550°C.Les mesures catalytiques ont mis en évidence l’oxydation de CH4 en CO2 après passage sur le catalyseur pour tous leséchantillons. L’efficacité catalytique est maximale et l’énergie d’activation est la plus faible pour l’échantillon x=1.8 ;ceci est lié à la plus grande surface spécifique, et au plus fort taux de sites actifs pour cette composition.Les ferrites de cobalt élaborées présentent une conduction de type électronique avec un comportement semi conducteurjusqu’à 500-600°C et un comportement métallique au-delà. Les variations de conductivité d’une composition à l’autres’expliquent par les variations du nombre de paires [Co2+,Fe3+].Les nanoparticules ont un comportement superparamagnétique quelle que soit la composition. Ce comportement estdû principalement à un effet de taille et de forme, et à une distribution cationique différente entre les deux types desites tétraédriques et octaédriques de la structure spinelle. Ces ferrites présentent une aimantation à saturation prochede celle de l’état massif, du fait de la grande qualité cristalline attribuée à la méthode d’élaboration mise au point.This work is devoted to the synthesis and the study of the physical properties of cobalt ferrite nanomaterials. Thecobalt ferrite nanopowders (CoxFe3-xO4 , x=0.6,1,1.2,1.8 ) were synthesized by a new solvo thermal chemical route.The nanopowders are highly crystallized, very homogeneous in size and chemical composition. The nanopowderssizes are ranged from 4 nm for high cobalt content to 7 nm for low cobalt content. They are single phased, with thespinel structure, and a cell parameter varying with the cobalt content. The cobalt ferrites do not oxidize, when heatedunder air. For compositions near x=1, the cobalt ferrites are stable when heated under air up to 900°C, as for the othercompositions, phase transformations occur above 550°C.The catalytic measurements have shown the oxidation of CH4 into CO2 in presence of the catalyst for all thecompositions. Cobalt ferrite with composition x=1.8, presents the lowest activation energy and the best catalyticefficiency; this can be related to the great specific surface and the high rate of active sites for this composition.Concerning the conduction properties, the cobalt ferrites exhibit a semiconductor character up to 500-600 ° C and ametallic one above. Changes in conductivity from a composition to another are explained by changes in the number ofpairs [Co2+, Fe3+].A superparamagnetic behaviour was evidenced whatever the composition. This is due for one part to a size and shapeeffect and for the other part to different cationic distribution between tetrahedral and octahedral sites. These ferriteshave a saturation magnetization close to that of the massive state, because of the high crystallinity of the nanopowders,attributed to the synthesis method developed in this work

Ferrites de cobalt nanostructurés ; élaboration, caractérisation, propriétés catalytiques, électriques et magnétiques

This work is devoted to the synthesis and the study of the physical properties of cobalt ferrite nanomaterials. Thecobalt ferrite nanopowders (CoxFe3-xO4 , x=0.6,1,1.2,1.8 ) were synthesized by a new solvo thermal chemical route.The nanopowders are highly crystallized, very homogeneous in size and chemical composition. The nanopowderssizes are ranged from 4 nm for high cobalt content to 7 nm for low cobalt content. They are single phased, with thespinel structure, and a cell parameter varying with the cobalt content. The cobalt ferrites do not oxidize, when heatedunder air. For compositions near x=1, the cobalt ferrites are stable when heated under air up to 900°C, as for the othercompositions, phase transformations occur above 550°C.The catalytic measurements have shown the oxidation of CH4 into CO2 in presence of the catalyst for all thecompositions. Cobalt ferrite with composition x=1.8, presents the lowest activation energy and the best catalyticefficiency; this can be related to the great specific surface and the high rate of active sites for this composition.Concerning the conduction properties, the cobalt ferrites exhibit a semiconductor character up to 500-600 ° C and ametallic one above. Changes in conductivity from a composition to another are explained by changes in the number ofpairs [Co2+, Fe3+].A superparamagnetic behaviour was evidenced whatever the composition. This is due for one part to a size and shapeeffect and for the other part to different cationic distribution between tetrahedral and octahedral sites. These ferriteshave a saturation magnetization close to that of the massive state, because of the high crystallinity of the nanopowders,attributed to the synthesis method developed in this work.Ce travail est consacré à l’élaboration et l’étude des propriétés catalytiques, électriques et magnétiques denanomatériaux à base de ferrite de cobalt. Les nanopoudres de ferrite de cobalt (CoxFe3-xO4 , x=0.6,1,1.2,1.8 ) ont étéélaborées par une nouvelle méthode chimique solvo-thermale. Les nanopoudres obtenues sont très bien cristallisées ontdes tailles de particules qui varient avec le taux de cobalt entre 4 et 7 nm et sont très homogènes en composition. Lesnanopoudres de ferrites de cobalt sont monophasées, de structure spinelle avec un paramètre de maille qui varie enfonction du taux de cobalt. Les nanopoudres de ferrites de cobalt ne s’oxydent pas sous air et en température .Lesnanopoudres de composition proches de x=1 sont stables jusqu’à 900°C, alors que pour de plus forts écarts à lastoechiométrie, des transformations de phase ont lieu au delà de 550°C.Les mesures catalytiques ont mis en évidence l’oxydation de CH4 en CO2 après passage sur le catalyseur pour tous leséchantillons. L’efficacité catalytique est maximale et l’énergie d’activation est la plus faible pour l’échantillon x=1.8 ;ceci est lié à la plus grande surface spécifique, et au plus fort taux de sites actifs pour cette composition.Les ferrites de cobalt élaborées présentent une conduction de type électronique avec un comportement semi conducteurjusqu’à 500-600°C et un comportement métallique au-delà. Les variations de conductivité d’une composition à l’autres’expliquent par les variations du nombre de paires [Co2+,Fe3+].Les nanoparticules ont un comportement superparamagnétique quelle que soit la composition. Ce comportement estdû principalement à un effet de taille et de forme, et à une distribution cationique différente entre les deux types desites tétraédriques et octaédriques de la structure spinelle. Ces ferrites présentent une aimantation à saturation prochede celle de l’état massif, du fait de la grande qualité cristalline attribuée à la méthode d’élaboration mise au point

Synthesis and microstructure of cobalt ferrite nanoparticles

International audienceCobalt ferrites (CoxFe3-xO4) nanoparticles with various compositions were synthesized by a new non-aqueous synthesis method. The cobalt ferrites were characterized by X-rays diffraction, and transmission electron microscopy coupled with energy dispersive spectroscopy. The nanoparticles are highly crystallized, with a homogeneous chemical composition. The particle size varies from 4 nm up to 7.5 nm, depending on the cobalt content. The smallest particles, with a size of 4 nm, are obtained for high cobalt content. These particles have also the highest micro-structural strain. Catalytic measurements were realized using Fourier Transform Infrared Spectroscopy. The lowest activation energy and the highest conversion rate are obtained for Co1.8Fe2.4O4, in the 400-500°C temperature range

Nanoparticles of Cobalt Ferrite for NH3 Sensing

The electrical response of cobalt ferrites CoxFe3-xO4 nanopowders was tested in presence of ammonia. The morphology, shape and chemical composition of the powder was fully characterized by transmission electron microscopy. Fast response, good sensitivity and good reversibility were evidenced, with detection even at 5 ppm NH3. Gas selectivity depends on the cobalt amount, x, in cobalt ferrite powders

Toward Sustainable Water Resources Management in the Tunisian Citrus Sector: Impact of Pricing Policies on Water Resources Reallocation

This study aims to analyse Tunisian farmers’ ability to pay (ATP) in a citrus area and propose a penalising price strategy based on the block-pricing process to decrease over-irrigation without affecting farmers’ incomes. The methodology is based on the residual imputation approach to determine farmers’ ATP, a stochastic production frontier to estimate the technical efficiency to determine optimal water irrigation quantity and calculation of the price elasticity of demand for an effective penalty and the Gini index before and after penalisation to study equity improvement. A survey was carried out on a sample of 147 citrus farms in the Nabeul Governorate, Northeastern Tunisia. The technical efficiency analysis confirms that an optimal quantity of 5000 m3/ha guarantees the maximisation of yields and profits. Above this quantity, the amount of overused water could be penalised without significantly affecting farmers’ incomes. Results also reveal that water overconsumption represents 28% of available resources and the ATP varies according to technical efficiency. Therefore, the proposed penalty system could reduce water overconsumption by 44.56% without deteriorating agricultural welfare. To improve water management as well as farmers’ welfare, this study recommends an increase in the technical efficiency level of farms to optimise all production factors for any implemented pricing policy

Toward Sustainable Water Resources Management in the Tunisian Citrus Sector: Impact of Pricing Policies on Water Resources Reallocation

This study aims to analyse Tunisian farmers’ ability to pay (ATP) in a citrus area and propose a penalising price strategy based on the block-pricing process to decrease over-irrigation without affecting farmers’ incomes. The methodology is based on the residual imputation approach to determine farmers’ ATP, a stochastic production frontier to estimate the technical efficiency to determine optimal water irrigation quantity and calculation of the price elasticity of demand for an effective penalty and the Gini index before and after penalisation to study equity improvement. A survey was carried out on a sample of 147 citrus farms in the Nabeul Governorate, Northeastern Tunisia. The technical efficiency analysis confirms that an optimal quantity of 5000 m3/ha guarantees the maximisation of yields and profits. Above this quantity, the amount of overused water could be penalised without significantly affecting farmers’ incomes. Results also reveal that water overconsumption represents 28% of available resources and the ATP varies according to technical efficiency. Therefore, the proposed penalty system could reduce water overconsumption by 44.56% without deteriorating agricultural welfare. To improve water management as well as farmers’ welfare, this study recommends an increase in the technical efficiency level of farms to optimise all production factors for any implemented pricing policy