Synthèse non-hydrolytique et structure de nanoparticules de ZrO2

This work deals with the synthesis and the structural characterization of zirconium oxide nanoparticles (ZrO2) as well as their size/structure relationships. We elaborated nanoparticles with a size inferior to 5 nm and a narrow size distribution using a non-hydrolytic solvothermal sol-gel route. Classical X-ray diffraction was used to evaluate the crystallite size via Rietveld refinement and X-ray total scattering to extract the pair distribution functions (PDF) of the samples for structural analysis.We succeeded in synthesizing crystalline nanoparticles of ZrO2 with a size of about 3 nm and quasi mono-dispersed. We showed that an adjusted addition of sodium hydroxide into the reaction mixture was pertinent to obtain a well crystallized and single-phase nanoparticles exhibiting an average monoclinic or tetragonal structure in benzaldehyde or in benzyl alcohol, respectively. Finally, the dilution of benzyl alcohol by anisole, an inert solvent, lead to the fine tuning of average crystallite size of the nanoparticles from 3.2 nm to 2 nm according to the TEM investigation.Those three major samples prepared in alkalinized benzaldehyde, benzyl alcohol, or anisole were subjected to complete structural analysis. According to their PDF analysis, these three samples offer an insight to the understanding of structural properties of such small particles.The experimental PDF of the benzaldehyde-prepared sample coincide with the refined PDF of a monoclinic structural model. However, the experimental PDF of the benzyl alcohol-prepared sample does not conform to any of the known polymorphs of ZrO2 having a fluorite-derived structure but rather it has an average tetragonal structure and a monoclinic distortion at the short-range order. Lastly, the experimental PDF of the anisole-prepared sample has large structural distortion at the medium-range order but has monoclinic structural features at the short-range order. We then subjected the anisole-prepared sample by thermally assisted ageing (3 to 24 days) and addition of varied amounts ex-situ water (0.3 to 5% volume content). We observed that the nanoparticles evolve from a phase containing high disorder (3 days) to a state of higher structural order (24 days) that fits with the average tetragonal structure while maintaining a monoclinic distortion at the short-range order. Similarly, the addition of ex-situ water onto the reaction mixture promoted a faster crystallization and promotes the onset of peaks that aligns with the monoclinic structure. However, the formation of monoclinic phases was inhibited by the presence of sodium hydroxide but limited to about 2% volume water content and higher than this amount lead to the formation of large particles with monoclinic structure.Ce travail traite de la synthèse et de la caractérisation structurale de nanoparticules d'oxyde de zirconium (ZrO2) ainsi que de leurs relations taille/structure. Nous avons élaboré des nanoparticules de taille inférieure à 5 nm avec une distribution de taille étroite en utilisant une voie sol-gel non hydrolytique solvothermale. La diffraction des rayons X classique a été utilisée pour évaluer la taille des cristallites via des affinements de Rietveld et la diffusion totale des rayons X pour extraire les fonctions de distribution des paires (PDF) des échantillons et effectuer leur analyse structurale.Nous avons réussi à synthétiser des nanoparticules cristallines de ZrO2 d'une taille d'environ 3 nm et quasi mono-disperses. Nous avons montré qu'une addition d'hydroxyde de sodium dans le mélange réactionnel était pertinente pour obtenir des nanoparticules bien cristallisées et monophasées présentant une structure moyenne soit monoclinique soit tétragonale en fonction du solvant utilisé, respectivement dans le benzaldéhyde ou dans l'alcool benzylique. Enfin, la dilution de l'alcool benzylique par l'anisole, un solvant inerte, conduit au contrôle fin de la taille moyenne des nanoparticules de 3,2 nm à 2 nm selon l'étude MET.Ces trois échantillons principaux préparés dans le benzaldéhyde alcalinisé, l'alcool benzylique ou l'anisole ont été soumis à une analyse structurale complète. Selon leur analyse PDF, ces trois échantillons offrent un aperçu de la compréhension des propriétés structurales de ces petites particules.La PDF expérimental de l'échantillon préparé avec du benzaldéhyde coïncide avec la PDF affinée d'un modèle structural monoclinique. Cependant, la PDF expérimentale de l'échantillon préparé avec de l'alcool benzylique n'est conforme à aucun des polymorphes connus de ZrO2 ayant une structure dérivée de la fluorine, mais présente plutôt une structure tétragonale moyenne avec des distorsions monocliniques à l'ordre local. Enfin, la PDF expérimentale de l'échantillon préparé avec de l'anisole présente de fortes distorsions structurales dans le domaine de l'ordre à moyenne distance, mais aussi une structure de type monoclinique à l'ordre local.Ensuite, l'échantillon préparé avec l'anisole a été soumis à un vieillissement assisté thermiquement (3 à 24 jours) et on a ajouté des quantités variables d'eau ex-situ (teneur en volume de 0,3 à 5%). Nous avons observé que les nanoparticules évoluaient d'une phase contenant un désordre élevé (3 jours) à une structure mieux cristallisée (24 jours) correspondant à une structure tétragonale moyenne tout en maintenant une distorsion monoclinique à l'ordre local. De manière similaire, l'addition d'eau ex-situ sur le mélange réactionnel favorise une cristallisation plus rapide et favorise l'apparition de pics typiques de la structure monoclinique. Cependant, la formation de phase monoclinique a été inhibée par la présence d'hydroxyde de sodium, mais limitée à environ 2% en volume d'eau, et une valeur plus élevée que cette quantité conduit à la formation de grandes particules de structure monoclinique

Solvent effect in the nonaqueous synthesis of ZrO2 nanoparticles under alkaline conditions

International audienceThis work deals with the synthesis of zirconium dioxide (ZrO2) nanoparticles (NPs) in different solvents and their structural characterization for better understanding the oxygen donor solvent/zirconium precursor/NPs structure relationships. By selecting solvents over their capacity to produce different crystalline states from alkalinized zirconium alkoxide, spherical nanoparticles with a size of about 1.3 to 3 nm and a narrow size distribution were elaborated using a nonaqueous solvothermal sol-gel route. Conventional X-ray diffraction (XRD) was used to determine the average structure and crystallite size of the nanoparticles. Well crystallized and single-phased nanoparticles with average monoclinic and tetragonal structure were obtained with benzaldehyde and benzyl alcohol respectively, and a much distorted structure was observed for the synthesis in anisole. The atomic pair distribution functions (PDF) of the samples were also analyzed to access the local structure of the nanoparticles. The PDF of the benzaldehyde-prepared sample is consistent with the monoclinic structure. However, the local structure of nanoparticles synthesized with benzyl alcohol does not fully conform to the tetragonal structure observed by XRD but exhibits monoclinic-like distortions. Lastly, the anisole-prepared nanoparticles present large structural distortions at the medium-range and monoclinic local structural features. The restructuring of this last sample was studied by posttreatments in different solvents and leads to the expression of the tetragonal polymorph. Moreover, it seems that the main structural features are obtained in the early stages of the nanoparticles' formation

Synthesis and characterization of ultrasmall zirconia particles via nonhydrolyticsolvothermal technique.

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Synthesis of ultrasmall zirconia particles via a modified non-hydrolytic sol-gel route

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Low temperature solvothermal synthesis of nanosized oxidic particles

International audienceAdvancement in modern science and applied technologies is brought to its current noteworthy mechanical, electronic and thermal properties because of researches in synthesis in nanocrystalline materials. Interestingly, variation in sizes becomes distinctive when sizes reaches nanoscale which exhibits properties that are atomic and bulk characteristics 1. Although studies in nanomaterials have taken huge steps over the last few decades but its structure determination which is crucial in modelling its properties is still at its earlier stages 2. Modelling of nanosized particles require a comparable experimental counterpart. Hence, it is vital to synthesize high quality nanosized particles in order to obtain a realistic comparison. However, there are limitations in synthesizing such particles due to the difficulty in maintaining control over its size and its phase purity. Solvothermal synthesis following a nonhydrolytic route offers a promising solution to this problem since it is able to produce high purity and good homogeneity 3 in size. In this work, we present ultrasmall zirconia nanoparticles that are well crystallized and the absent utilization of surfactants. Structural and morphological analysis of the samples were done using classical X-ray diffraction and transmission electron microscopy. Result indicates that we were able to manipulate the phase purity of our samples from a dual to single phase. Similarly, by varying its synthesis conditions we were able to exhibit a good control over the size which arranges from ~5.0 to ~1.0 nm. In addition, the modified solvothermal synthesis allowed us to synthesize nanoparticles are very low temperatures about 80 o C with good compositional purity

Detrimental Effect and Neutralization of in Situ Produced Water on Zirconia Nanoparticles Obtained by a Nonaqueous Sol–Gel Method

International audienceIn this work, the phase purity and size of zirconia nanocrystals samples were studied in terms of zirconium concentration, added water content and subsequent use of a post solvothermal treatment. The progressive tetragonal-to-monoclinic transformation of zirconia sample was observed to be strongly related to the water content of the alcoholic medium. But more surprisingly, it has been shown that even under initially anhydrous conditions and for particle size below 5 nm, the phase purity of the samples was deteriorated by a side-reaction of alcohol dehydration catalyzed by the surface of the nanoparticles (NPs). Since the phase transformation is essentially driven by the water content of the reaction mixture, we have shown that it was possible to recover an excellent phase purity without the help of any usual dopant

Liquid phase synthesis of materials -nanostructures and characterization

The liquid phase synthesis of materials is a powerful way to obtain samples which could otherwise notbe prepared by conventional methods. This is particularly useful when dealing with nanomaterials, asstarting from metal organic precursors favors a better control of the nucleation/growth phenomena.In this work, the synthesis of nanoparticles of metal oxide compositions was performed using nonhydrolyticsolvothermal synthesis in the ZrO2, ZnO, SnO2 and TiO2 systems. The objective was to obtaincrystallized particles with uniform sizes of less than 5 nm to correlate the synthesis parameters, sizeand local structure of the samples. Indeed, for such small sizes, the bulk-based structural models donot apply anymore and specific properties are identified.For all the selected chemical systems, the synthesis of very small crystallized particles was successful.In this case, the control of water and thermal parameters is as important as the choice of the reagents.The samples were analyzed by conventional X-ray diffraction, pair distribution function andtransmission electron microscopy in order to determine their average and local structure as well astheir morphology. Locally, the atomic structure of the particles are clearly different from the bulkstructures when the sizes are inferior to 5 nm

Synthesis, characterization and structural modeling of intercalated and nanostructured hydrotalcite compounds.

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