An alternative route for metal hydrogenation has been investigated: cold plasma hydrogen implanta... more An alternative route for metal hydrogenation has been investigated: cold plasma hydrogen implantation on polyol-made transition metal nanoparticles. This treatment applied to a challenging system, Ni–H, induces a re-ordering of the metal lattice, and superstructure lines have been observed by both Bragg–Brentano and grazing incidence X-ray diffraction. The resulting intermetallic structure is similar to those obtained by very high-pressure hydrogenation of nickel and prompt us to suggest that plasma-based hydrogen implantation in nanometals is likely to generate unusual metal hydride, opening new opportunities in chemisorption hydrogen storage. Typically, almost isotropic in shape and about 30 nm sized hexagonal-packed Ni2H single crystals were produced starting from similarly sized cubic face-centred Ni polycrystals.
Monodisperse ruthenium nanoparticles were prepared by reduction of RuCl3 in 1,2-propanediol. The ... more Monodisperse ruthenium nanoparticles were prepared by reduction of RuCl3 in 1,2-propanediol. The mean particle size was controlled by appropriate choice of the reduction temperature and the acetate ion concentration. Colloidal solutions in toluene were obtained by coating the metal particles with dodecanethiol. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XANES and EXAFS for the Ru K-absorption edge) were performed on particles of two different diameters, 2 and 4 nm, and in different environments, polyol/acetate or thiol. For particles stored in polyol/acetate XPS studies revealed superficial oxidation limited to one monolayer and a surface coating containing mostly acetate ions. Analysis of the EXAFS spectra showed both oxygen and ruthenium atoms around the ruthenium atoms with a Ru-Ru coordination number N smaller than the bulk value, as expected for fine particles. In the case of 2 nm acetate-capped particles N is consistent with particles made up of a metallic core and an oxidized monolayer. For 2 nm thiol-coated particles, a Ru-S bond was evidenced by XPS and XAS. For the 4 nm particles XANES and XPS studies showed that most of the ruthenium atoms are in the zerovalent state. Nevertheless, in both cases, when capped with thiol, the Ru-Ru coordination number inferred from EXAFS is much smaller than for particles of the same size stored in polyol. This is attributed to a structural disorganization of the particles by thiol chemisorption. HRTEM studies confirm the marked dependence of the structural properties of the ruthenium particles on their chemical environment; they show the acetate-coated particles to be single crystals, whereas the thiol-coated particles appear to be polycrystalline.
The formation of silver nanopetal-Fe3O4 poly-nanocrystals assemblies and the use of the resulting... more The formation of silver nanopetal-Fe3O4 poly-nanocrystals assemblies and the use of the resulting hetero-nanostructures as active substrates for Surface Enhanced Raman Spectroscopy (SERS) application are here reported. In practice, about 180 nm sized polyol-made Fe3O4 spheres, constituted by 10 nm sized crystals, were functionalized by (3-aminopropyl)triethoxysilane (APTES) to become positively charged, which can then electrostatically interact with negatively charged silver seeds. Silver petals were formed by seed-mediated growth in presence of Ag+ cations and self-assembly, using L-ascorbic acid (L-AA) and polyvinyl pyrrolidone (PVP) as mid-reducing and stabilizing agents, respectively. The resulting plasmonic structure provides a rough surface with plenty of hot spots able to locally enhance significantly any applied electrical field. Additionally, they exhibited a high enough saturation magnetization with Ms = 9.7 emu g−1 to be reversibly collected by an external magnetic field,...
TiO2/Ti nanostructures were synthesized by the hydrothermal route. Based on the operating conditi... more TiO2/Ti nanostructures were synthesized by the hydrothermal route. Based on the operating conditions, namely the heating time and temperature, the microstructure of the produced titania was successfully varied from very thick and short nanofibers to very thin and long nanowires. UV-Visible diffuse reflectance spectroscopy also evidenced a net dependency of the optical properties of the produced semiconducting films, and consequently their photocatalytic and photoelectrocatalytic activity, to their synthesis conditions. Typically, the photodegradation of methylene blue in water under UV irradiation as well as the oxidation of water without additional bias were assessed and showed different efficiencies according the type of tested film.
Current biomedical imaging techniques are crucial for the diagnosis of various diseases. Each ima... more Current biomedical imaging techniques are crucial for the diagnosis of various diseases. Each imaging technique uses specific probes that, although each one has its own merits, do not encompass all the functionalities required for comprehensive imaging (sensitivity, non-invasiveness, etc.). Bimodal imaging methods are therefore rapidly becoming an important topic in advanced healthcare. This bimodality can be achieved by successive image acquisitions involving different and independent probes, one for each mode, with the risk of artifacts. It can be also achieved simultaneously by using a single probe combining a complete set of physical and chemical characteristics, in order to record complementary views of the same biological object at the same time. In this scenario, and focusing on bimodal magnetic resonance imaging (MRI) and optical imaging (OI), probes can be engineered by the attachment, more or less covalently, of a contrast agent (CA) to an organic or inorganic dye, or by d...
Abstract Nickel doped zinc sulfide (Ni:ZnS) thin films are deposited on glass substrates by chemi... more Abstract Nickel doped zinc sulfide (Ni:ZnS) thin films are deposited on glass substrates by chemical bath deposition (CBD) for different Ni concentrations (0, 6, 12 and 18 at.-%). X-ray diffraction (XRD) patterns of undoped and Ni doped layers show a cubic structure with (111) preferred orientation. For the highest Ni concentration an impurity phase is detected and assigned to NiS compound. Fourier transform infrared (FTIR) analysis proves the existence of some residues in the films. X-ray photoelectron spectroscopy (XPS) reveals the formation of ZnS. The morphological study by scanning electron microscopy (SEM) shows important changes in layers topography. Transmittance (T) and reflectance (R) data reveal an enhancement for 6 at.-% and 12 at.-% dopant concentrations. Finally, photoluminescence (PL) properties show a decrease of the emission intensity with an increment of Ni content until 12 at.-%. Then, an increase of the PL intensity is observed with further increase of Ni amount.
CoO submicrometer-sized pseudo-single crystals were produced in polyol thanks to an oriented aggr... more CoO submicrometer-sized pseudo-single crystals were produced in polyol thanks to an oriented aggregation crystal growth driven by the polyol molecules themselves.
Using solar radiation to fuel catalytic processes is often regarded as the solution to our energy... more Using solar radiation to fuel catalytic processes is often regarded as the solution to our energy needs. However, developing effective photocatalysts active under visible light has proven to be difficult, often due to toxicity, instability, and high cost of suitable catalysts. We engineered a novel photoactive nanomaterial obtained by the spontaneous electrostatic coupling of carbon nanodots with [P2W18O62]6- , a molecular catalyst belonging to the class of polyoxometalates. While the former are used as photosensitizers, the latter was chosen for its ability to catalyze reductive reactions such as dye decomposition and water-splitting. We find the electron transfer within the nanohybrid to be so efficient that a charge-separated state is formed within 120 femtoseconds from photon absorption. These results are a cornerstone towards the engineering of a new class of nano-devices, non-toxic, low-cost, and able to carry out solar-driven catalytic processes.
This study investigated the steady shear flow and viscoelastic properties of composite materials ... more This study investigated the steady shear flow and viscoelastic properties of composite materials elaborated by introduction of positively charged polyol-made maghemite nanoparticles (NPs) in aqueous solution s of negatively charged sodium alginate polymers. Two different ligands were covalently attached to the particle surface, the 3-aminopropyl triethyloxysilane (APTES) and the 3,4-dihydroxyphenylethylamine (DOPA), and their effect on the general rheological and magneto-rheological behaviors of the resulting composites was highlighted. Indeed, the experiments revealed that the increase of low shear viscosity and the viscoelastic moduli in the linear viscoelastic domain can be correlated to the nature of the two ligands inducing either compact or loose aggregates between positively charged NPs and negatively charged biopolymer chains. These field-induced microstructures have been qualitatively observed by optical microscopy under applied magnetic field.
Fe-glycolate wires with micrometer-scale lengths can be synthesized by the polyol process. Althou... more Fe-glycolate wires with micrometer-scale lengths can be synthesized by the polyol process. Although the as-produced wires are in the paramagnetic state at room temperature, they are transformed into ferrimagnetic iron oxides and ferromagnetic metallic iron wires by reductive annealing. The shape of the wires is unchanged by reductive annealing, and it is possible to control the magnetic properties of the resulting wire-shaped ferri/ferromagnets by adjusting the annealing conditions. Consequently, the reductive annealing of polyol-derived Fe-glycolate wires is an effective material-processing route for the production of magnetic wires.
Magnetic materials are crucial for the efficiency of the conversion-storage-transport-reconversio... more Magnetic materials are crucial for the efficiency of the conversion-storage-transport-reconversion energy chain, and the enhancement of their performance has an important impact on technological development. The present work explores the possibility of preparing hetero-nano-structured ceramics based on magnetic oxides, by coupling a ferrimagnetic phase (F) with an antiferromagnetic one (AF) on the nanometric scale. The field-assisted sintering technique or SPS (Spark-Plasma Sintering), adopted at this purpose, ensures the preservation of nano-sized crystals within the final solid structure. The aim is to establish how exchange bias may affect the resulting nano-consolidates and to investigate the potential of this process to increase the total magnetic anisotropy of the CoFe2O4grains, and thus their coercive field, while keeping the saturation magnetization the same. The structure, microstructure and magnetic properties of the ceramics obtained were studied by several techniques. Th...
Materials science & engineering. C, Materials for biological applications, 2019
Polygonal-shaped about 75 nm sized and highly crystallized Eu-doped β-NaYF particles were directl... more Polygonal-shaped about 75 nm sized and highly crystallized Eu-doped β-NaYF particles were directly prepared under mild conditions using the polyol process. A set of operating parameters were optimized for such a purpose. A conventional heating under reflux for 30 min of a mixture of Y(III) and Eu(III) acetate, ammonium fluoride, sodium hydroxide and oleic acid (OA) dissolved in ethyleneglycol offered a pertinent material processing route if a large excess of NHF and an enough amount of OA were used. Typically, the former parameter provides an exclusive stabilization of the desired β allotropic form, while the latter allows a significant size decrease of the particles. Thanks to their coating by a double OA layer, the produced particles exhibited a hydrophilic surface feature when dispersed in water and when excited under UV light they emitted a very intense red photoluminescence. Additionally, they did not evidence any accurate cytotoxicity when incubated with healthy human foreskin...
Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials
The compound [Eu5(C2H4O2)6(CH3CO2)3] n was synthesized by dissolving acetate europium salt in eth... more The compound [Eu5(C2H4O2)6(CH3CO2)3] n was synthesized by dissolving acetate europium salt in ethylene glycol solvent and heating under reflux for a short time. Its structure was solved ab initio from synchrotron powder diffraction data using optimization methods in direct space. The compound has a very large unit-cell volume of 23679 Å3 and the highest centred cubic symmetry space group, Ia{\bar 3}d (No. 230). The porous metal–organic framework structure is similar to those usually observed in zeolites, with pores volumes of 82 Å3, which is of potential interest for gas storage.
An alternative route for metal hydrogenation has been investigated: cold plasma hydrogen implanta... more An alternative route for metal hydrogenation has been investigated: cold plasma hydrogen implantation on polyol-made transition metal nanoparticles. This treatment applied to a challenging system, Ni–H, induces a re-ordering of the metal lattice, and superstructure lines have been observed by both Bragg–Brentano and grazing incidence X-ray diffraction. The resulting intermetallic structure is similar to those obtained by very high-pressure hydrogenation of nickel and prompt us to suggest that plasma-based hydrogen implantation in nanometals is likely to generate unusual metal hydride, opening new opportunities in chemisorption hydrogen storage. Typically, almost isotropic in shape and about 30 nm sized hexagonal-packed Ni2H single crystals were produced starting from similarly sized cubic face-centred Ni polycrystals.
Monodisperse ruthenium nanoparticles were prepared by reduction of RuCl3 in 1,2-propanediol. The ... more Monodisperse ruthenium nanoparticles were prepared by reduction of RuCl3 in 1,2-propanediol. The mean particle size was controlled by appropriate choice of the reduction temperature and the acetate ion concentration. Colloidal solutions in toluene were obtained by coating the metal particles with dodecanethiol. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XANES and EXAFS for the Ru K-absorption edge) were performed on particles of two different diameters, 2 and 4 nm, and in different environments, polyol/acetate or thiol. For particles stored in polyol/acetate XPS studies revealed superficial oxidation limited to one monolayer and a surface coating containing mostly acetate ions. Analysis of the EXAFS spectra showed both oxygen and ruthenium atoms around the ruthenium atoms with a Ru-Ru coordination number N smaller than the bulk value, as expected for fine particles. In the case of 2 nm acetate-capped particles N is consistent with particles made up of a metallic core and an oxidized monolayer. For 2 nm thiol-coated particles, a Ru-S bond was evidenced by XPS and XAS. For the 4 nm particles XANES and XPS studies showed that most of the ruthenium atoms are in the zerovalent state. Nevertheless, in both cases, when capped with thiol, the Ru-Ru coordination number inferred from EXAFS is much smaller than for particles of the same size stored in polyol. This is attributed to a structural disorganization of the particles by thiol chemisorption. HRTEM studies confirm the marked dependence of the structural properties of the ruthenium particles on their chemical environment; they show the acetate-coated particles to be single crystals, whereas the thiol-coated particles appear to be polycrystalline.
The formation of silver nanopetal-Fe3O4 poly-nanocrystals assemblies and the use of the resulting... more The formation of silver nanopetal-Fe3O4 poly-nanocrystals assemblies and the use of the resulting hetero-nanostructures as active substrates for Surface Enhanced Raman Spectroscopy (SERS) application are here reported. In practice, about 180 nm sized polyol-made Fe3O4 spheres, constituted by 10 nm sized crystals, were functionalized by (3-aminopropyl)triethoxysilane (APTES) to become positively charged, which can then electrostatically interact with negatively charged silver seeds. Silver petals were formed by seed-mediated growth in presence of Ag+ cations and self-assembly, using L-ascorbic acid (L-AA) and polyvinyl pyrrolidone (PVP) as mid-reducing and stabilizing agents, respectively. The resulting plasmonic structure provides a rough surface with plenty of hot spots able to locally enhance significantly any applied electrical field. Additionally, they exhibited a high enough saturation magnetization with Ms = 9.7 emu g−1 to be reversibly collected by an external magnetic field,...
TiO2/Ti nanostructures were synthesized by the hydrothermal route. Based on the operating conditi... more TiO2/Ti nanostructures were synthesized by the hydrothermal route. Based on the operating conditions, namely the heating time and temperature, the microstructure of the produced titania was successfully varied from very thick and short nanofibers to very thin and long nanowires. UV-Visible diffuse reflectance spectroscopy also evidenced a net dependency of the optical properties of the produced semiconducting films, and consequently their photocatalytic and photoelectrocatalytic activity, to their synthesis conditions. Typically, the photodegradation of methylene blue in water under UV irradiation as well as the oxidation of water without additional bias were assessed and showed different efficiencies according the type of tested film.
Current biomedical imaging techniques are crucial for the diagnosis of various diseases. Each ima... more Current biomedical imaging techniques are crucial for the diagnosis of various diseases. Each imaging technique uses specific probes that, although each one has its own merits, do not encompass all the functionalities required for comprehensive imaging (sensitivity, non-invasiveness, etc.). Bimodal imaging methods are therefore rapidly becoming an important topic in advanced healthcare. This bimodality can be achieved by successive image acquisitions involving different and independent probes, one for each mode, with the risk of artifacts. It can be also achieved simultaneously by using a single probe combining a complete set of physical and chemical characteristics, in order to record complementary views of the same biological object at the same time. In this scenario, and focusing on bimodal magnetic resonance imaging (MRI) and optical imaging (OI), probes can be engineered by the attachment, more or less covalently, of a contrast agent (CA) to an organic or inorganic dye, or by d...
Abstract Nickel doped zinc sulfide (Ni:ZnS) thin films are deposited on glass substrates by chemi... more Abstract Nickel doped zinc sulfide (Ni:ZnS) thin films are deposited on glass substrates by chemical bath deposition (CBD) for different Ni concentrations (0, 6, 12 and 18 at.-%). X-ray diffraction (XRD) patterns of undoped and Ni doped layers show a cubic structure with (111) preferred orientation. For the highest Ni concentration an impurity phase is detected and assigned to NiS compound. Fourier transform infrared (FTIR) analysis proves the existence of some residues in the films. X-ray photoelectron spectroscopy (XPS) reveals the formation of ZnS. The morphological study by scanning electron microscopy (SEM) shows important changes in layers topography. Transmittance (T) and reflectance (R) data reveal an enhancement for 6 at.-% and 12 at.-% dopant concentrations. Finally, photoluminescence (PL) properties show a decrease of the emission intensity with an increment of Ni content until 12 at.-%. Then, an increase of the PL intensity is observed with further increase of Ni amount.
CoO submicrometer-sized pseudo-single crystals were produced in polyol thanks to an oriented aggr... more CoO submicrometer-sized pseudo-single crystals were produced in polyol thanks to an oriented aggregation crystal growth driven by the polyol molecules themselves.
Using solar radiation to fuel catalytic processes is often regarded as the solution to our energy... more Using solar radiation to fuel catalytic processes is often regarded as the solution to our energy needs. However, developing effective photocatalysts active under visible light has proven to be difficult, often due to toxicity, instability, and high cost of suitable catalysts. We engineered a novel photoactive nanomaterial obtained by the spontaneous electrostatic coupling of carbon nanodots with [P2W18O62]6- , a molecular catalyst belonging to the class of polyoxometalates. While the former are used as photosensitizers, the latter was chosen for its ability to catalyze reductive reactions such as dye decomposition and water-splitting. We find the electron transfer within the nanohybrid to be so efficient that a charge-separated state is formed within 120 femtoseconds from photon absorption. These results are a cornerstone towards the engineering of a new class of nano-devices, non-toxic, low-cost, and able to carry out solar-driven catalytic processes.
This study investigated the steady shear flow and viscoelastic properties of composite materials ... more This study investigated the steady shear flow and viscoelastic properties of composite materials elaborated by introduction of positively charged polyol-made maghemite nanoparticles (NPs) in aqueous solution s of negatively charged sodium alginate polymers. Two different ligands were covalently attached to the particle surface, the 3-aminopropyl triethyloxysilane (APTES) and the 3,4-dihydroxyphenylethylamine (DOPA), and their effect on the general rheological and magneto-rheological behaviors of the resulting composites was highlighted. Indeed, the experiments revealed that the increase of low shear viscosity and the viscoelastic moduli in the linear viscoelastic domain can be correlated to the nature of the two ligands inducing either compact or loose aggregates between positively charged NPs and negatively charged biopolymer chains. These field-induced microstructures have been qualitatively observed by optical microscopy under applied magnetic field.
Fe-glycolate wires with micrometer-scale lengths can be synthesized by the polyol process. Althou... more Fe-glycolate wires with micrometer-scale lengths can be synthesized by the polyol process. Although the as-produced wires are in the paramagnetic state at room temperature, they are transformed into ferrimagnetic iron oxides and ferromagnetic metallic iron wires by reductive annealing. The shape of the wires is unchanged by reductive annealing, and it is possible to control the magnetic properties of the resulting wire-shaped ferri/ferromagnets by adjusting the annealing conditions. Consequently, the reductive annealing of polyol-derived Fe-glycolate wires is an effective material-processing route for the production of magnetic wires.
Magnetic materials are crucial for the efficiency of the conversion-storage-transport-reconversio... more Magnetic materials are crucial for the efficiency of the conversion-storage-transport-reconversion energy chain, and the enhancement of their performance has an important impact on technological development. The present work explores the possibility of preparing hetero-nano-structured ceramics based on magnetic oxides, by coupling a ferrimagnetic phase (F) with an antiferromagnetic one (AF) on the nanometric scale. The field-assisted sintering technique or SPS (Spark-Plasma Sintering), adopted at this purpose, ensures the preservation of nano-sized crystals within the final solid structure. The aim is to establish how exchange bias may affect the resulting nano-consolidates and to investigate the potential of this process to increase the total magnetic anisotropy of the CoFe2O4grains, and thus their coercive field, while keeping the saturation magnetization the same. The structure, microstructure and magnetic properties of the ceramics obtained were studied by several techniques. Th...
Materials science & engineering. C, Materials for biological applications, 2019
Polygonal-shaped about 75 nm sized and highly crystallized Eu-doped β-NaYF particles were directl... more Polygonal-shaped about 75 nm sized and highly crystallized Eu-doped β-NaYF particles were directly prepared under mild conditions using the polyol process. A set of operating parameters were optimized for such a purpose. A conventional heating under reflux for 30 min of a mixture of Y(III) and Eu(III) acetate, ammonium fluoride, sodium hydroxide and oleic acid (OA) dissolved in ethyleneglycol offered a pertinent material processing route if a large excess of NHF and an enough amount of OA were used. Typically, the former parameter provides an exclusive stabilization of the desired β allotropic form, while the latter allows a significant size decrease of the particles. Thanks to their coating by a double OA layer, the produced particles exhibited a hydrophilic surface feature when dispersed in water and when excited under UV light they emitted a very intense red photoluminescence. Additionally, they did not evidence any accurate cytotoxicity when incubated with healthy human foreskin...
Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials
The compound [Eu5(C2H4O2)6(CH3CO2)3] n was synthesized by dissolving acetate europium salt in eth... more The compound [Eu5(C2H4O2)6(CH3CO2)3] n was synthesized by dissolving acetate europium salt in ethylene glycol solvent and heating under reflux for a short time. Its structure was solved ab initio from synchrotron powder diffraction data using optimization methods in direct space. The compound has a very large unit-cell volume of 23679 Å3 and the highest centred cubic symmetry space group, Ia{\bar 3}d (No. 230). The porous metal–organic framework structure is similar to those usually observed in zeolites, with pores volumes of 82 Å3, which is of potential interest for gas storage.
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Papers by Souad Ammar-Merah