We report the synthesis of Mn–Zn ferrite (MZFO) nanoparticles (NPs) by the polyol process and the... more We report the synthesis of Mn–Zn ferrite (MZFO) nanoparticles (NPs) by the polyol process and their consolidation by Spark Plasma Sintering (SPS) technique at relatively low temperature and short time, namely 500 °C for 10 min. NPs were obtained as perfectly epitaxied aggregated nanoclusters forming a kind of spherical pseudo-single-crystals of about 40 nm in size. The results on NPs consolidation by SPS underlined the importance of this clustering on the grain growth mechanism. Grain growth proceeds by coalescing nanocrystalline aggregates into single grain of almost the same average size, thus leading to a high density ceramic. Due to magnetic exchange interactions between grains, the produced ceramic does not exhibit thermal relaxation whereas their precursor polyol-made NPs are superparamagnetic.
This study aims to characterize nanoparticles with different compositions and structures as well ... more This study aims to characterize nanoparticles with different compositions and structures as well as seeing their evolutions over time in a natural environment such as Seine river water (Paris, France). Face centered cubic (fcc) and hexagonal (hcp) CdS as well as hexagonal (hcp) ZnO nanoparticles were synthesized by the Polyol method. CdS nanoparticles (i) cfc structure: are agglomerated, present 100 nm length with heterogeneous diameter and 10 m2 g(-1) specific surface area (S(g)) from Brunauer Emett and Teller (BET) measurements; (ii) hcp structure: 20 nm and S(g) = 67 m2 g(-1). ZnO hcp nanoparticles presents 50 nm length and 15 nm diameter and S(g) = 54 m2 g(-1). These results are in agreement with X-ray diffraction (XRD), and small angle X-ray scattering (SAXs). After 48 h interaction with Seine river water, cryo-TEM analysis showed that ZnO nanoparticles form spherical agglomerates with 300 nm diameter; CdS nanoparticles (fcc) are agglomerated presenting large diameters (> 500 nm); and CdS nanoparticles (hcp) are not agglomerated and present the same characteristics of the starting material. After 168h of contact with Seine river water, CdS (fcc) presents only 14% of dissolution, CdS (hcp) presents both 60% dissolution and 30% reprecipitation in a cadmium carbonate form and finally almost 90% of ZnO nanoparticles are dissolved.
ABSTRACT Nanocrystalline films were directly prepared by spray deposition of a preformed polyol-b... more ABSTRACT Nanocrystalline films were directly prepared by spray deposition of a preformed polyol-based Ni0.8Zn0.2Fe2O4 sol on a moderately heated glass substrate. The microstructural and magnetic properties of these films are investigated by X-ray diffraction, scanning electron microscopy and magnetic measurements on a Super Quanducting Interference Devices magnetometer. They are compared with those of nanoparticles precipitated from the sol, and with those of film subsequently annealed in air at 400°C. The films and the powder exhibit superparamagnetic behaviour with a blocking temperature which increases from the powder to the as-produced film to the annealed film, in agreement with increasing stress and/or crystal size. They are ferrimagnetic at low temperature with a hysteresis feature strongly dependent on the synthesis conditions. The stresses induced in the film upon deposition undoubtedly correlate with a large grain boundaries volume which contributes to the Hc, the coercitive field, increase and Msat, the saturation magnetization, decrease.
The potential ecotoxicological impact of ZnO nanostructured films was investigated using common A... more The potential ecotoxicological impact of ZnO nanostructured films was investigated using common Anabaena flos-aquae, Calothrix pulvinata cyanobacteria and Euglena gracilis euglenoid microalgae. The pre-formed ZnO nanoparticles were synthesized in di(ethylene glycol) medium by forced hydrolysis of ionic Zn 2+ salts. Particle size and shape were controlled by addition of protective agents such as tri-n-octylphosphine oxide and polyoxyethylene stearyl ether. ZnO nanostructured films were directly prepared by spray deposition of pre-formed polyol-based ZnO nanoparticles (ZnO, ZnO-TOPO and ZnO-Brij-76) at 250°C heated glass substrate. Another sample was prepared from zinc acetate in di(ethylene glycol) diluted in ethanol medium without nanoparticles (ZnO-SOL). In this case, ZnO nanostructured film was formed directly on the glass substrate at the same temperature. Water contact angle on ZnO-based films showed that nanostructured ZnO films containing ZnO nanoparticles prepared without protective agent or with tri-n-octylphosphine oxide present a hydrophobic character while the ones containing nanoparticles prepared using polyoxyethylene stearyl ether or the control sample are hydrophilic. Here we showed that (i) the use of protective agents, (ii) the surface properties of the films and (iii) the nature of the biological system can strongly influence the ecotoxicological studies. Epifluorescence microscopy analyses and Live/Dead tests showed that all films are toxic for Euglena gracilis. In the case of Anabaena flos-aquae and Calothrix pulvinata, tri-n-octylphosphine oxide and polyoxyethylene stearyl ether molecules can prevent ZnO nanoparticle toxicity.
Nickel -zinc ferrite monodisperse nanoparticles are synthesized by forced hydrolysis in diethylen... more Nickel -zinc ferrite monodisperse nanoparticles are synthesized by forced hydrolysis in diethylenglycol. FC and ZFC susceptibility curves suggest that they present superparmagnetic behaviour with a blocking temperature between 63 and 15 K depending on the zinc content. The saturation magnetization of the nanocrystals at 5 K is very close to that of bulk materials, and very high compared to that of similar particles prepared by other chemical routes. High Resolution Transmission Electron Microscopy and In-field Mössbauer studies show clearly that these relatively high values are mainly due to: (i) the high crystalline quality of the particles and (ii) a cation distribution different from the classical distribution encountered in the bulk material. 2 Z. Beji et al.: Synthesis of nickel -zinc ferrite nanoparticles in polyol
Silver nanostructured films were directly prepared by spray deposition of preformed polyol-based ... more Silver nanostructured films were directly prepared by spray deposition of preformed polyol-based Ag-PVP nanoparticles. These homogeneous films of high optical quality were tested as SERS-active substrates. Laser excitation at 514.5 nm within the red part of the plasmon band leads to intense and reproducible SERS spectra of acridine, used as the probe molecule. From SERS measurements at different pH values, it was possible to determine the apparent pK(a) of acridine and to obtain specific surface properties of the film. Finally, these SERS titrations along with enhancement factor estimates allowed us to further depict the nature of the films.
ABSTRACT Static-spray deposition of a polyol-based sol, containing nanoparticles of NiZn ferrite,... more ABSTRACT Static-spray deposition of a polyol-based sol, containing nanoparticles of NiZn ferrite, on a moderately heated glass support, has been used to generate crystalline thin films. The films exhibit superparamagnetic behavior with a blocking temperature, which decreases as the zinc content increases, due to their nanocrystalline character. At low temperature, the films are ferrimagnetic; the saturation magnetization and the coercivity depend markedly on both the zinc content and the microstructure. (c) 2008 American Institute of Physics.
Ferrite nanoparticles of composition Zn 0.5 Ni 0.5 Fe 2 O 4 were prepared by forced hydrolysis in... more Ferrite nanoparticles of composition Zn 0.5 Ni 0.5 Fe 2 O 4 were prepared by forced hydrolysis in a polyol (polyol process) from the corresponding iron, nickel, and zinc acetates. Synthesis conditions allowed for obtaining polycrystalline epitaxial clusters of about 22 nm in size with an average crystal size of about 5 nm. These powders were subsequently consolidated by spark plasma sintering (SPS) technique under a pressure of 80 MPa and temperatures in the 350 to 500 C range for short periods (5 to 10 min). Densities reached 92% to 94% of the theoretical density. Particle size remained smaller than 61 nm, even for the highest temperature. Ferromagnetic resonance experiments at 77 K showed broadened resonance lines. In contrast with powdered nanoparticles, these high-density bodies can be used in many high-frequency applications.
ABSTRACT In the present study, we report the synthesis of Zn-ferrite nanoparticles by a soft chem... more ABSTRACT In the present study, we report the synthesis of Zn-ferrite nanoparticles by a soft chemical coprecipitation method. The magnetic properties of Zn ferrite are sensitive to their average crystallite size ( d) which can be varied by altering the synthesis conditions. The d value was controlled by the pH of the solution which is related to the number of moles of OH- ions (x ). The XRD pattern of as synthesized samples showed single phase spinel structure. The estimated d is in the range of 2 to 12 nm. The magnetization studies showed that the sample with d = 2 nm is paramagnetic whereas the samples with d >; 2 nm exhibited superparamagnetic behavior. The magnetization at 10 kG increases from 2.6 to 21.4 emu/g as d increases from 2 to 12 nm. The temperature dependent studies for the sample with d = 12 nm shows symmetric spectra with single resonance peak of Lorentzian shape. As the temperature decreases an additional peak at lower field side of the main signal appears. The g value and the linewidth (ΔHPP) increase with decrease in temperature indicating the increase in antiferromagnetic (AFM) interactions between the ions in tetrahedral and the octahedral sites.
... J. Gavard§, K. Kacem , F. Villain||, J.-M. Gren che#, F. Chau, and S. Ammar*. ... Mn 1−x Zn... more ... J. Gavard§, K. Kacem , F. Villain||, J.-M. Gren che#, F. Chau, and S. Ammar*. ... Mn 1−x Zn x Fe 2 O 4 nanoparticles (MZFOs) are probably the most promising materials. Indeed, they are stable in air and water and are able, due to their reduced size, to form aqueous colloids. ...
ABSTRACT Zn1−xCoxO nanocrystals were produced by forced hydrolysis in diethyleneglycol. The as-pr... more ABSTRACT Zn1−xCoxO nanocrystals were produced by forced hydrolysis in diethyleneglycol. The as-produced crystals are paramagnetic. However, heating at 400 °C under a nitrogen atmosphere for 1 h induces ferromagnetism at room temperature, characterized by coercive field (0.38 kOe) and magnetization at 10 kOe (0.10 μB/Co) similar to the values reported recently for nanocrystalline Co:ZnO aggregates. To understand this evolution, we have characterized the samples by chemical and physical analyses including X-ray diffraction (XRD), transmission electron microscopy (TEM), UV−visible−IR absorption spectroscopy, magnetic measurements, and EPR experiments. These analyses show that the Co ions are incorporated into the wurtzite structure, forming a Zn1−xCoxO solid solution. X-ray diffraction and electron microscopy failed to detect secondary phases, neither before nor after the thermal treatment. However, the shape of the nanoparticles is modified and becomes more spherical upon annealing, which gives evidence of an important diffusion of atomic species. X-band electron paramagnetic resonance (EPR) reveals the presence of magnetic clusters in the annealed samples. Both the magnetic and optical properties show that these are Co clusters that have grown at the expense of the cobalt diluted in the host matrix. The thermal treatment survey performed by thermogravimetric analysis coupled with mass spectrometry and IR spectroscopy gives evidence of desorption of organic species and liberation of oxygen from the surface of the particles. This study then suggests that the origin of the magnetism believed to be intrinsic to the material in many prior works is extrinsic in nature and is due to the diffusion of cobalt and oxygen species at the surface of the particles, where Co forms nanoclusters while most of the oxygen is liberated in the annealing process.
We report the synthesis of Mn–Zn ferrite (MZFO) nanoparticles (NPs) by the polyol process and the... more We report the synthesis of Mn–Zn ferrite (MZFO) nanoparticles (NPs) by the polyol process and their consolidation by Spark Plasma Sintering (SPS) technique at relatively low temperature and short time, namely 500 °C for 10 min. NPs were obtained as perfectly epitaxied aggregated nanoclusters forming a kind of spherical pseudo-single-crystals of about 40 nm in size. The results on NPs consolidation by SPS underlined the importance of this clustering on the grain growth mechanism. Grain growth proceeds by coalescing nanocrystalline aggregates into single grain of almost the same average size, thus leading to a high density ceramic. Due to magnetic exchange interactions between grains, the produced ceramic does not exhibit thermal relaxation whereas their precursor polyol-made NPs are superparamagnetic.
This study aims to characterize nanoparticles with different compositions and structures as well ... more This study aims to characterize nanoparticles with different compositions and structures as well as seeing their evolutions over time in a natural environment such as Seine river water (Paris, France). Face centered cubic (fcc) and hexagonal (hcp) CdS as well as hexagonal (hcp) ZnO nanoparticles were synthesized by the Polyol method. CdS nanoparticles (i) cfc structure: are agglomerated, present 100 nm length with heterogeneous diameter and 10 m2 g(-1) specific surface area (S(g)) from Brunauer Emett and Teller (BET) measurements; (ii) hcp structure: 20 nm and S(g) = 67 m2 g(-1). ZnO hcp nanoparticles presents 50 nm length and 15 nm diameter and S(g) = 54 m2 g(-1). These results are in agreement with X-ray diffraction (XRD), and small angle X-ray scattering (SAXs). After 48 h interaction with Seine river water, cryo-TEM analysis showed that ZnO nanoparticles form spherical agglomerates with 300 nm diameter; CdS nanoparticles (fcc) are agglomerated presenting large diameters (> 500 nm); and CdS nanoparticles (hcp) are not agglomerated and present the same characteristics of the starting material. After 168h of contact with Seine river water, CdS (fcc) presents only 14% of dissolution, CdS (hcp) presents both 60% dissolution and 30% reprecipitation in a cadmium carbonate form and finally almost 90% of ZnO nanoparticles are dissolved.
ABSTRACT Nanocrystalline films were directly prepared by spray deposition of a preformed polyol-b... more ABSTRACT Nanocrystalline films were directly prepared by spray deposition of a preformed polyol-based Ni0.8Zn0.2Fe2O4 sol on a moderately heated glass substrate. The microstructural and magnetic properties of these films are investigated by X-ray diffraction, scanning electron microscopy and magnetic measurements on a Super Quanducting Interference Devices magnetometer. They are compared with those of nanoparticles precipitated from the sol, and with those of film subsequently annealed in air at 400°C. The films and the powder exhibit superparamagnetic behaviour with a blocking temperature which increases from the powder to the as-produced film to the annealed film, in agreement with increasing stress and/or crystal size. They are ferrimagnetic at low temperature with a hysteresis feature strongly dependent on the synthesis conditions. The stresses induced in the film upon deposition undoubtedly correlate with a large grain boundaries volume which contributes to the Hc, the coercitive field, increase and Msat, the saturation magnetization, decrease.
The potential ecotoxicological impact of ZnO nanostructured films was investigated using common A... more The potential ecotoxicological impact of ZnO nanostructured films was investigated using common Anabaena flos-aquae, Calothrix pulvinata cyanobacteria and Euglena gracilis euglenoid microalgae. The pre-formed ZnO nanoparticles were synthesized in di(ethylene glycol) medium by forced hydrolysis of ionic Zn 2+ salts. Particle size and shape were controlled by addition of protective agents such as tri-n-octylphosphine oxide and polyoxyethylene stearyl ether. ZnO nanostructured films were directly prepared by spray deposition of pre-formed polyol-based ZnO nanoparticles (ZnO, ZnO-TOPO and ZnO-Brij-76) at 250°C heated glass substrate. Another sample was prepared from zinc acetate in di(ethylene glycol) diluted in ethanol medium without nanoparticles (ZnO-SOL). In this case, ZnO nanostructured film was formed directly on the glass substrate at the same temperature. Water contact angle on ZnO-based films showed that nanostructured ZnO films containing ZnO nanoparticles prepared without protective agent or with tri-n-octylphosphine oxide present a hydrophobic character while the ones containing nanoparticles prepared using polyoxyethylene stearyl ether or the control sample are hydrophilic. Here we showed that (i) the use of protective agents, (ii) the surface properties of the films and (iii) the nature of the biological system can strongly influence the ecotoxicological studies. Epifluorescence microscopy analyses and Live/Dead tests showed that all films are toxic for Euglena gracilis. In the case of Anabaena flos-aquae and Calothrix pulvinata, tri-n-octylphosphine oxide and polyoxyethylene stearyl ether molecules can prevent ZnO nanoparticle toxicity.
Nickel -zinc ferrite monodisperse nanoparticles are synthesized by forced hydrolysis in diethylen... more Nickel -zinc ferrite monodisperse nanoparticles are synthesized by forced hydrolysis in diethylenglycol. FC and ZFC susceptibility curves suggest that they present superparmagnetic behaviour with a blocking temperature between 63 and 15 K depending on the zinc content. The saturation magnetization of the nanocrystals at 5 K is very close to that of bulk materials, and very high compared to that of similar particles prepared by other chemical routes. High Resolution Transmission Electron Microscopy and In-field Mössbauer studies show clearly that these relatively high values are mainly due to: (i) the high crystalline quality of the particles and (ii) a cation distribution different from the classical distribution encountered in the bulk material. 2 Z. Beji et al.: Synthesis of nickel -zinc ferrite nanoparticles in polyol
Silver nanostructured films were directly prepared by spray deposition of preformed polyol-based ... more Silver nanostructured films were directly prepared by spray deposition of preformed polyol-based Ag-PVP nanoparticles. These homogeneous films of high optical quality were tested as SERS-active substrates. Laser excitation at 514.5 nm within the red part of the plasmon band leads to intense and reproducible SERS spectra of acridine, used as the probe molecule. From SERS measurements at different pH values, it was possible to determine the apparent pK(a) of acridine and to obtain specific surface properties of the film. Finally, these SERS titrations along with enhancement factor estimates allowed us to further depict the nature of the films.
ABSTRACT Static-spray deposition of a polyol-based sol, containing nanoparticles of NiZn ferrite,... more ABSTRACT Static-spray deposition of a polyol-based sol, containing nanoparticles of NiZn ferrite, on a moderately heated glass support, has been used to generate crystalline thin films. The films exhibit superparamagnetic behavior with a blocking temperature, which decreases as the zinc content increases, due to their nanocrystalline character. At low temperature, the films are ferrimagnetic; the saturation magnetization and the coercivity depend markedly on both the zinc content and the microstructure. (c) 2008 American Institute of Physics.
Ferrite nanoparticles of composition Zn 0.5 Ni 0.5 Fe 2 O 4 were prepared by forced hydrolysis in... more Ferrite nanoparticles of composition Zn 0.5 Ni 0.5 Fe 2 O 4 were prepared by forced hydrolysis in a polyol (polyol process) from the corresponding iron, nickel, and zinc acetates. Synthesis conditions allowed for obtaining polycrystalline epitaxial clusters of about 22 nm in size with an average crystal size of about 5 nm. These powders were subsequently consolidated by spark plasma sintering (SPS) technique under a pressure of 80 MPa and temperatures in the 350 to 500 C range for short periods (5 to 10 min). Densities reached 92% to 94% of the theoretical density. Particle size remained smaller than 61 nm, even for the highest temperature. Ferromagnetic resonance experiments at 77 K showed broadened resonance lines. In contrast with powdered nanoparticles, these high-density bodies can be used in many high-frequency applications.
ABSTRACT In the present study, we report the synthesis of Zn-ferrite nanoparticles by a soft chem... more ABSTRACT In the present study, we report the synthesis of Zn-ferrite nanoparticles by a soft chemical coprecipitation method. The magnetic properties of Zn ferrite are sensitive to their average crystallite size ( d) which can be varied by altering the synthesis conditions. The d value was controlled by the pH of the solution which is related to the number of moles of OH- ions (x ). The XRD pattern of as synthesized samples showed single phase spinel structure. The estimated d is in the range of 2 to 12 nm. The magnetization studies showed that the sample with d = 2 nm is paramagnetic whereas the samples with d >; 2 nm exhibited superparamagnetic behavior. The magnetization at 10 kG increases from 2.6 to 21.4 emu/g as d increases from 2 to 12 nm. The temperature dependent studies for the sample with d = 12 nm shows symmetric spectra with single resonance peak of Lorentzian shape. As the temperature decreases an additional peak at lower field side of the main signal appears. The g value and the linewidth (ΔHPP) increase with decrease in temperature indicating the increase in antiferromagnetic (AFM) interactions between the ions in tetrahedral and the octahedral sites.
... J. Gavard§, K. Kacem , F. Villain||, J.-M. Gren che#, F. Chau, and S. Ammar*. ... Mn 1−x Zn... more ... J. Gavard§, K. Kacem , F. Villain||, J.-M. Gren che#, F. Chau, and S. Ammar*. ... Mn 1−x Zn x Fe 2 O 4 nanoparticles (MZFOs) are probably the most promising materials. Indeed, they are stable in air and water and are able, due to their reduced size, to form aqueous colloids. ...
ABSTRACT Zn1−xCoxO nanocrystals were produced by forced hydrolysis in diethyleneglycol. The as-pr... more ABSTRACT Zn1−xCoxO nanocrystals were produced by forced hydrolysis in diethyleneglycol. The as-produced crystals are paramagnetic. However, heating at 400 °C under a nitrogen atmosphere for 1 h induces ferromagnetism at room temperature, characterized by coercive field (0.38 kOe) and magnetization at 10 kOe (0.10 μB/Co) similar to the values reported recently for nanocrystalline Co:ZnO aggregates. To understand this evolution, we have characterized the samples by chemical and physical analyses including X-ray diffraction (XRD), transmission electron microscopy (TEM), UV−visible−IR absorption spectroscopy, magnetic measurements, and EPR experiments. These analyses show that the Co ions are incorporated into the wurtzite structure, forming a Zn1−xCoxO solid solution. X-ray diffraction and electron microscopy failed to detect secondary phases, neither before nor after the thermal treatment. However, the shape of the nanoparticles is modified and becomes more spherical upon annealing, which gives evidence of an important diffusion of atomic species. X-band electron paramagnetic resonance (EPR) reveals the presence of magnetic clusters in the annealed samples. Both the magnetic and optical properties show that these are Co clusters that have grown at the expense of the cobalt diluted in the host matrix. The thermal treatment survey performed by thermogravimetric analysis coupled with mass spectrometry and IR spectroscopy gives evidence of desorption of organic species and liberation of oxygen from the surface of the particles. This study then suggests that the origin of the magnetism believed to be intrinsic to the material in many prior works is extrinsic in nature and is due to the diffusion of cobalt and oxygen species at the surface of the particles, where Co forms nanoclusters while most of the oxygen is liberated in the annealing process.
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