Procédé de recuit protégé appliqué à des nanoparticules d'oxyde de fer : étude des relations structure / propriétés magnétiques

Because of their promising applications, particularly in the field of biomedicine, many research activities are currently focused in understanding and improving the magnetic properties of iron oxide nanoparticles. The large surface/volume ratio, inherent to the size reduction at the nanometer scale, and crystalline defects have a significant influence on the magnetic properties of these particles, because they give rise to weakly coupled and misaligned spins, which are responsible for low saturation magnetization values. In the course of this PhD project, a strategy of protected annealing was investigated to improve the crystallinity and/or to change the local composition of maghemite and cobalt ferrite nanoparticles, without agglomeration or grain growth. A diamagnetic, refractory and inert sol-gel silica matrix was selected. The high-temperature annealing of the composite samples was first used to study the impact of various structural defects on the magnetic properties. We showed that for maghemite nanoparticles, ordering of Fe vacancies and changes in the surface state, as a result of dehydration, had opposite effects. Vacancy ordering predominates for particles of 14 nm and tends to increase magnetization values, while the removal of surface hydroxyl groups, predominant for particles of 7 nm, induces the propagation of the outer shell made of misaligned spins toward the center of the particles, thus decreasing magnetization values. In the case of cobalt ferrite, the Co-Fe ions distribution may also have an impact on spin misalignment. However, an 800°C annealing did not induced a large increase in inversion degree, probably because of the refractory nature of CoFe2O4. This strategy of protected annealing also allowed modulating the magnetic properties of maghemite particles upon cobalt doping. A progressive increase of the anisotropy constant, up to 3.5 times, was observed as a result of the diffusion of Co2+ ions into the spinel structure.Du fait de leurs nombreuses applications, notamment dans le domaine biomédical, beaucoup d'études actuelles visent à la compréhension et à l'amélioration des propriétés magnétiques de nanoparticules d'oxyde de fer de structure spinelle. En effet, le fort rapport surface/volume, inhérent à la réduction en taille dans le domaine du nanomètre, et la présence de défauts cristallins ont une influence déterminante sur les propriétés magnétiques des particules. Ceci s'explique notamment par la présence de spins en situation de couplage faible, désalignés, qui sont responsables d'une réduction de l'aimantation à saturation. Lors de cette thèse, une stratégie de " recuit protégé " de nanoparticules de maghémite et de ferrite de cobalt a été mise en œuvre afin d'améliorer leur cristallinité et/ou de changer leur composition locale et ce sans grossissement ni agglomération des grains. Une matrice de silice produite par voie sol-gel a été retenue car elle est diamagnétique mais également réfractaire et inerte. Le recuit à haute température des composites a tout d'abord permis d'étudier l'impact de différents défauts structuraux sur les propriétés magnétiques. Il a ainsi été montré que pour des nanoparticules de maghémite, la mise en ordre des lacunes de fer et les changements d'état de surface liés à la déshydroxylation des particules avaient des effets antagonistes. Le premier effet, prédominant pour des particules de 14 nm, tend à augmenter la valeur de l'aimantation, alors que le second, prépondérant pour les particules de 7 nm, induit une propagation de la couche de spins désalignés de surface et donc une diminution de l'aimantation. Dans le cas du ferrite de cobalt, un autre paramètre, la répartition cationique pourrait avoir un impact sur le désalignement des spins. Un recuit à 800°C n'a cependant pas permis une forte augmentation du taux d'inversion, probablement du fait du caractère réfractaire de CoFe2O4. Cette même stratégie de recuit protégé a également permis de moduler les propriétés magnétiques de particules de maghémite par dopage avec des ions Co2+. Une augmentation progressive de la constante d'anisotropie, jusqu'à un facteur 3,5, a ainsi été observée du fait de la diffusion des ions Co2+ dans la structure spinelle

Procédé de recuit protégé appliqué à des nanoparticules d'oxyde de fer (étude des relations structure / propriétés magnétiques)

Du fait de leurs nombreuses applications, notamment dans le domaine biomédical, beaucoup d'études actuelles visent à la compréhension et à l'amélioration des propriétés magnétiques de nanoparticules d'oxyde de fer de structure spinelle. En effet, le fort rapport surface/volume, inhérent à la réduction en taille dans le domaine du nanomètre, et la présence de défauts cristallins ont une influence déterminante sur les propriétés magnétiques des particules. Ceci s'explique notamment par la présence de spins en situation de couplage faible, désalignés, qui sont responsables d'une réduction de l'aimantation à saturation. Lors de cette thèse, une stratégie de " recuit protégé " de nanoparticules de maghémite et de ferrite de cobalt a été mise en œuvre afin d'améliorer leur cristallinité et/ou de changer leur composition locale et ce sans grossissement ni agglomération des grains. Une matrice de silice produite par voie sol-gel a été retenue car elle est diamagnétique mais également réfractaire et inerte. Le recuit à haute température des composites a tout d'abord permis d'étudier l'impact de différents défauts structuraux sur les propriétés magnétiques. Il a ainsi été montré que pour des nanoparticules de maghémite, la mise en ordre des lacunes de fer et les changements d'état de surface liés à la déshydroxylation des particules avaient des effets antagonistes. Le premier effet, prédominant pour des particules de 14 nm, tend à augmenter la valeur de l'aimantation, alors que le second, prépondérant pour les particules de 7 nm, induit une propagation de la couche de spins désalignés de surface et donc une diminution de l'aimantation. Dans le cas du ferrite de cobalt, un autre paramètre, la répartition cationique pourrait avoir un impact sur le désalignement des spins. Un recuit à 800C n'a cependant pas permis une forte augmentation du taux d'inversion, probablement du fait du caractère réfractaire de CoFe2O4. Cette même stratégie de recuit protégé a également permis de moduler les propriétés magnétiques de particules de maghémite par dopage avec des ions Co2+. Une augmentation progressive de la constante d'anisotropie, jusqu'à un facteur 3,5, a ainsi été observée du fait de la diffusion des ions Co2+ dans la structure spinelleBecause of their promising applications, particularly in the field of biomedicine, many research activities are currently focused in understanding and improving the magnetic properties of iron oxide nanoparticles. The large surface/volume ratio, inherent to the size reduction at the nanometer scale, and crystalline defects have a significant influence on the magnetic properties of these particles, because they give rise to weakly coupled and misaligned spins, which are responsible for low saturation magnetization values. In the course of this PhD project, a strategy of protected annealing was investigated to improve the crystallinity and/or to change the local composition of maghemite and cobalt ferrite nanoparticles, without agglomeration or grain growth. A diamagnetic, refractory and inert sol-gel silica matrix was selected. The high-temperature annealing of the composite samples was first used to study the impact of various structural defects on the magnetic properties. We showed that for maghemite nanoparticles, ordering of Fe vacancies and changes in the surface state, as a result of dehydration, had opposite effects. Vacancy ordering predominates for particles of 14 nm and tends to increase magnetization values, while the removal of surface hydroxyl groups, predominant for particles of 7 nm, induces the propagation of the outer shell made of misaligned spins toward the center of the particles, thus decreasing magnetization values. In the case of cobalt ferrite, the Co-Fe ions distribution may also have an impact on spin misalignment. However, an 800C annealing did not induced a large increase in inversion degree, probably because of the refractory nature of CoFe2O4. This strategy of protected annealing also allowed modulating the magnetic properties of maghemite particles upon cobalt doping. A progressive increase of the anisotropy constant, up to 3.5 times, was observed as a result of the diffusion of Co2+ ions into the spinel structurePALAISEAU-Polytechnique (914772301) / SudocSudocFranceF

Bioactive Glass Nanoparticles: From Synthesis to Materials Design for Biomedical Applications

Thanks to their high biocompatibility and bioactivity, bioactive glasses are very promising materials for soft and hard tissue repair and engineering. Because bioactivity and specific surface area intrinsically linked, the last decade has seen a focus on the development of highly porous and/or nano-sized materials. This review emphasizes the synthesis of bioactive glass nanoparticles and materials design strategies. The first part comprehensively covers mainly soft chemistry processes, which aim to obtain dispersible and monodispersed nanoparticles. The second part discusses the use of bioactive glass nanoparticles for medical applications, highlighting the design of materials. Mesoporous nanoparticles for drug delivery, injectable systems and scaffolds consisting of bioactive glass nanoparticles dispersed in a polymer, implant coatings and particle dispersions will be presented

Deeper Insights into a Bioactive Glass Nanoparticle Synthesis Protocol To Control Its Morphology, Dispersibility, and Composition

International audienc

Post-synthesis heat treatments of g-Fe2O3 nanoparticles embedded in a refractory matrix: From annealing of structural defects to doping

International audienceMagnetic nanoparticles (NPs) synthesized by low-temperature routes often present structural disorder, from extended defects to local rearrangements related to vacancy order or inversion in spinel ferrites. Post-synthesis heat treatments of preformed particles embedded in a refractory matrix are shown to modify magnetic anisotropy, either by annealing of crystal defects or by doping, while preserving the mean size and size distribution of the initial colloid. Such protected annealing of g-Fe2O3 NPs allows a large and tunable increase of the anisotropy constant upon cobalt doping, using a two-step protocol that may involve adsorption of Co(II) ions at the surface of g-Fe2O3 NPs followed by their dispersion in a silica matrix and heat treatments up to 600 C

Post-synthesis annealing of coprecipitated CoFe2O4 nanoparticles in silica matrix

International audienceCobalt ferrite nanoparticles (d ∼ 11 nm, σd = 0.5) produced by coprecipitation at room temperature are heat treated up to 1000 °C after a preliminary dispersion in a sol-gel silica matrix to avoid aggregation and coarsening. This protected annealing allows for a significant increase of the crystallinity of the particles, as demonstrated by combined x-ray diffraction and transmission electron microscopy experiments. A large increase in the coercive field value is reported, from 1.0 to 1.6 Tesla after annealing at 600 °C. This enhanced coercivity can be explained by the cumulative effect of an increased magnetic anisotropy and of a decreased saturation magnetization (Ms). Mössbauer spectroscopy experiments show that these evolutions of the Ms and anisotropy constant (K) values originate from a small increase in canting angles and in inversion degree, i.e. a displacement of Co2+ ions from tetrahedral to octahedral sites of the spinel lattice. This study emphasizes the little impact of an improved crystallinity on saturation magnetization and canting angle values in coprecipitated CoFe2O4 nanoparticles and highlights that the main source of magnetic disorder is associated with the distribution of Co and Fe within the cationic sites

Correlating the Effect of Composition and Textural Properties on Bioactivity for Pristine and Copper-Doped Binary Mesoporous Bioactive Glass Nanoparticles

Multifunctional substitutes for bone tissue engineering have gained significant interest in recent years in the aim to address the clinical challenge of treating large bone defects resulting from surgical procedures. Sol–gel mesoporous bioactive glass nanoparticles (MBGNs) have emerged as a promising solution due to their high reactivity and versatility. The effect of calcium content on MBGNs textural properties is well known. However, the relationship between their composition, textural properties, and reactivity has not yet been thoroughly discussed in existing studies, leading to divergent conclusions. In this study, pristine and copper-doped binary MGBNs were synthesized by a modified Stöber method, using a cationic surfactant as pore-templating agent. An opposite evolution between calcium content (12–26 wt%) and specific surface area (909–208 m2/g) was evidenced, while copper introduction (8.8 wt%) did not strongly affect the textural properties. In vitro bioactivity assessments conducted in simulated body fluid (SBF) revealed that the kinetics of hydroxyapatite (HAp) crystallization are mainly influenced by the specific surface area, while the composition primarily controls the quantity of calcium phosphate produced. The MBGNs exhibited a good bioactivity within 3 h, while Cu-MBGNs showed HAp crystallization after 48 h, along with a controlled copper release (up to 84 ppm at a concentration of 1 mg/mL). This comprehensive understanding of the interplay between composition, textural properties, and bioactivity, offers insights for the design of tailored MBGNs for bone tissue regeneration with additional biological and antibacterial effects

Influence of Protected Annealing on the Magnetic Properties of γ‑Fe₂O₃ Nanoparticles

It is usually considered that nanoparticles synthesized by low-temperature routes present structural disorder, from extended defects to local rearrangements (e.g., vacancy ordering or inversion in spinel ferrites), that may severely impact their magnetic properties. In the present work, we have investigated the influence of postsynthesis thermal treatments on 7-nm-sized γ-Fe₂O₃ nanoparticles prepared by room temperature coprecipitation of ferric and ferrous salts in alkaline medium, followed by the dispersion of the preformed particles in a sol–gel silica binder. Such protected annealing in a refractory matrix prevents coalescence and growth, thus preserving the mean size and size distribution of the pristine particles. Structural characterizations show that heat treatments up to 1000 °C turned the raw grains into well-crystallized particles without transformation into hematite. This strategy thus allows accounting for the influence of structural rearrangements on magnetic properties at fixed particle size. For such 7 nm particles, postsynthesis heat treatments were found to mainly influence the shell of misaligned spins at the surface

Elaboration of Superparamagnetic and Bioactive Multicore–Shell Nanoparticles (γ-Fe 2 O 3 @SiO 2 -CaO): A Promising Material for Bone Cancer Treatment

International audienceThe past few decades have seen the development of new bone cancer therapies, triggered by the discovery of new biomaterials. When the tumoral area is small and accessible, the common clinical treatment implies the tumor mass removal followed by bone reconstruction or consolidation with a bioceramic or a metallic scaffold. Even though the treatment also involves chemotherapy or radiotherapy, resurgence of cancer cells remains possible. We have thus designed a new kind of heterostructured nanobiomaterial, composed of SiO2-CaO bioactive glass as the shell and superparamagnetic γ-Fe2O3iron oxide as the core in order to combine the benefits of bone repair thanks to the glass bioactivity and of cancer cells destruction through magnetic hyperthermia (MH). These multifunctional core-shell nanoparticles (NPs) have been obtained using a two-stage procedure, involving the coprecipitation of 11 nm sized iron oxide NPs followed by their encapsulation inside a bioactive glass shell by sol-gel chemistry. The as-produced spherical multicore-shell NPs show a narrow size distribution of 73 ± 7 nm. Magnetothermal loss measurements by calorimetry under an alternating magnetic field and in vitrobioactivity assessment performed in SBF (Simulated Body Fluid) showed that these heterostructures exhibit a good heating capacity and a fast mineralization process (hydroxyapatite forming ability). In addition, their in vitrocytocompatibility, evaluated in the presence of Human Mesenchymal Stem Cells (h-MSCs) during 3 and 7 days, has been demonstrated. These firstfindings suggest that γ-Fe2O3@SiO2-CaO heterostructures are a promising biomaterial to fill bone defects resulting from bone tumors resection, as they have the ability to both repair bone tissue and to act as thermo-seeds for cancer therap

Introduction of Cobalt Ions in γ-Fe 2 O 3 Nanoparticles by Direct Coprecipitation or Postsynthesis Adsorption: Dopant Localization and Magnetic Anisotropy

International audienceThe influence of cobalt doping on the magnetic anisotropy of γ-Fe2O3 nanoparticles has been investigated using two different approaches: (i) simultaneous precipitation of Fe2+, Fe3+, and Co2+ precursors in water and (ii) adsorption of Co2+ ions onto the surface of preformed iron oxide particles followed by diffusion in the solid phase upon heat treatment. The incorporation of small amounts of Co dopants, less than 1 at %, was monitored by magnetization measurements combined with X-ray absorption spectroscopy experiments at the Co K-edge. These latter measurements were carried out in fluorescence mode using a crystal analyzer spectrometer for enhanced sensitivity. Analyses of the X-ray absorption fine structures allowed for unraveling the differences in local atomic structure and valence state of Co in the two series of samples. A thermally activated diffusion in the spinel lattice was observed in the 250−300 °C range, leading to a substantial increase in magnetocrystalline anisotropy. At higher annealing temperature, magnetic anisotropy was still found to increase due to an enhanced surface contribution associated with the dehydroxylation of terminal Fe atoms. This study not only provides direct correlations between magnetic anisotropy and dopant localization in Co-doped γ-Fe2O3 but also demonstrates for the first time that simultaneous coprecipitation of Fe2+, Fe3+, and Co2+ may actually lead to heterogeneous doping, with a significant part of the Co dopants adsorbed at the particle surface