Hydrolysis In Polyol Medium Research Articles

Chemical Inhomogeneity in Iron Oxide@CoO Core-Shell Nanoparticles: A Local Probe Study Using Zero-Field and In-Field 57Fe Mössbauer Spectrometry.

Core-shell magnetic nanoparticles type Fe3-xO₄ (≈10 nm)@CoO (≈3 nm) prepared by forced hydrolysis in polyol medium have been investigated through the combined use of dc magnetization measurements by SQUID and local analysis by 57Fe Mössbauer spectrometry. A shift of the hysteresis loop along the field axis was observed, which highlights the presence of exchange bias coupling in these nanoparticles. This exchange bias coupling is accompanied by an unexpected high value of coercive field in hysteresis loop in mode ZFC. A local probe study using both zero-field and in-field Mössbauer spectrometry reveals complex hyperfine structures. Great attention is paid to the fitting procedure: it is concluded that Fe3-xO₄@CoO nanoparticles result from a mixture of magnetite and maghemite phases in addition to the formation of an interface-like layer close to a cobalt ferrite. Such a structure explains both the high coercive field value observed by SQUID and the presence of exchange bias coupling.

New acetate-intercalated CoNiFe, ZnNiFe and CoZnFe layered double hydroxides: Synthesis by hydrolysis in polyol medium and characterization

New layered double hydroxides (LDHs) CoNiFe, ZnNiFe and CoZnFe with MII/MIII molar ratio of 3, with acetate ions in the interlayer region have been prepared by forced hydrolysis in polyol medium.The physico-chemical properties of all products were characterized by the methods of powder X-ray Diffraction, Infrared Spectroscopy, UV-Spectroscopy, Elemental analysis, Thermal analysis, Transmission Electron Microscopy and Scanning Electron Microscopy.It was found that all compounds present the typical features of hydrotalcite-like structure and exhibit a turbostratic character.The insertion of acetate anions into LDHs was confirmed and the interlayer spacing values were respectively 12.47, 13.64 and 14.69 Å for CoNiFe, ZnNiFe and CoZnFe.We notice that there is a difference between the interlayer spacing for all synthesized phases with and without zinc. This can be explained by a structural modification on the level of the layers and/ or different arrangement from the inserted species (anions + water) in the interlayer space for zinc materials.57Fe Mössbauer spectrometry allows concluding the presence of Fe3+ cations which occupy octahedral sites and confirming the absence of Fe2+ in the as-prepared compounds.

Nanocrystals of Zn(Fe)O-based diluted magnetic semi-conductor as potential luminescent and magnetic bimodal bioimaging probes

Nanocrystals of Zn(Fe)O-based diluted magnetic semi-conductor (nanoDMS) have been prepared by forced hydrolysis in polyol medium, using zinc and iron salts, and coated with carboxymethylpullulan (CMP). TEM studies revealed that CMP-nanoDMS are spherical, with average diameters on the order of 20 nm. Hydrodynamic diameters of about 75 nm were found in a physiological medium. NanoDMS were superparamagnetic at body temperature, and exhibited high saturation magnetization values (3.25 emu g−1). In aqueous suspensions, the colloids revealed high transverse proton relaxivities (T2) with an r2 value of 203 mM−1 s−1 (300 K, 1.41 T). Visible photoluminescent properties were evidenced with an excitation wavelength of 366 nm. No evidence of cell toxicity was found for human endothelial cells incubated with CMP-nanoDMS, at concentrations up to 100 μg mL−1 and for 48 h. No modification to the cytoskeleton was found up to 6 days of exposure. These hybrid nanomaterials could be considered as novel potential MR and luminescent bioimaging agents.

Effects of Oxide Nanoparticle Size and Shape on Electronic Structure, Charge Transport, and Recombination in Dye-Sensitized Solar Cell Photoelectrodes

Forced hydrolysis in polyol medium is a versatile synthesis method for the preparation of metal oxide particles with controlled properties. We investigated the D149-dye-sensitized solar cell (DSSC) performance of ZnO film electrodes prepared with four different types of nanoparticles having various sizes and morphologies. The photoanode dye loading has been determined, and the cells have been studied by impedance spectroscopy (IS) at various applied voltages. From the analysis of the IS spectra, the key functioning parameters of the various photoelectrodes such as trap-state distribution, electron-transfer time, and electron lifetime have been determined. The particle shape and size deeply influence the dye loading and the electronic structures of the trap-state levels localized below the conduction band minimum. Low open circuit voltage and fill factor are found in the case of small (8 nm) spherical particles because of very deep energy states related to large particle necking and high density of grain b...

Effect of spark plasma sintering process on the microstructure and mechanical properties of Nano crystalline hydroxyapatite ceramics prepared by hydrolysis in polyol medium

The aim of the study was to investigate the role of microstructure and porosity on the mechanical behaviour of sintered hydroxyapatite synthesized by polyol process. This process describes a new approach for the synthesis of hydroxyapatite nanoparticles, which involves precipitation and hydrolysis reactions conducted in polyol medium. In the present work a non-conventional technique, spark plasma sintering, was used to consolidate such nanocrystalline apatites at non-conventional, very low temperatures (T < 300°C) so as to preserve the surface hydrated layer present on the nanocrystals. The hydroxyapatite nanoparticles have been successfully conducted by spark plasma sintering process, resulting in a dense HA compacts. Besides, the sintering behaviour of hydroxyapatite powders at different temperatures ranging was studied. The microstructure, Vickers microhardness, nanoindentation and density are described. Finally, the resulting mechanical properties determined on the microwave sintered samples (E = 136 ±4 GPa, HV = 8.2 GPa, and KIC= 1.6 ±0.03 MPa m1/2) are significantly higher than those usually reported in the literature, whatever the sintering process, and could allow the use of hydroxyapatite for structural applications. Keywords: Hydroxyapatite; Polyol; Spark Plasma Sintering; Mechanical Properties.

Nanocrystalline Hydroxyapatite Ceramics Prepared by Hydrolysis in Polyol Medium, Microstructure and Mechanical Properties after Spark Plasma Sintering

This Letter describes a new approach for the synthesis of hydroxyapatite (HA) nanoparticles by polyol process has been successfully conducted by spark plasma sintering process, resulting in a dense hydroxyapatite compacts. Besides, the sintering behaviour of hydroxyapatite powders at different temperatures ranging from 800°C to 950°C at 50 MPa was studied. The microstructure, Vickers microhardness, fracture toughness and density are described. The suitable sintering condition under the pressure of 50 MPa is 900°C for 5 min. A maximum value of the density was reached at around 900°C, and then decreased with further increase in the temperature due to the decomposition of hydroxyapatite into β-tricalcium phosphates.

Preparation of cytocompatible luminescent and magnetic nanohybrids based on ZnO, Zn0.95Ni0.05O and core@shell ZnO@Fe2O3 polymer grafted nanoparticles for biomedical imaging

ZnO, Zn0.95Ni0.05O and core@shell ZnO@γ-Fe2O3 nanoparticles (NPs) have been prepared by forced hydrolysis in polyol medium and then coated via the “grafting from” approach with poly(sodium-4-styrenesulfonate) and poly(sodium-4-styrenesulfonate–co–sodium methacrylate) in the case of ZnO. The surface-initiated atom transfer radical polymerization occurred from the surface-functionalized NPs with α-bromoisobutyric acid as initiator. The polymer chains were grown from the surface to yield hybrid NPs with a 1–3-nm thick organic shell. FT-IR, TGA and electron microscopy evidenced the presence of a polymer layer on the surface of NPs. Magnetic and optical properties of bare and coated NPs have been measured. Eventually, the weak cytotoxicity of coated NPs on human endothelial cell allows considering their potentialities as new tools for nanomedicine and biomedical imaging.

Nanocrystalline hydroxyapatite ceramics prepared by hydrolysis in polyol medium

This Letter describes a new approach for the synthesis of hydroxyapatite nanoparticles, which involves precipitation and hydrolysis reactions conducted in polyol medium. In fact, ammonium-hydrogen phosphate and calcium nitrate were dissolved in polyol, and then heated at the boiling point of the polyol (ethane1, 2diol or propane1, 2diol). Besides, the phase and composition of the polycrystalline were studied by TGA/DTA, FT-IR, TEM and XRD techniques. The nanoparticles thus obtained present interesting morphological characters varying from needle to very thin platelet. Moreover, the hydroxyapatite prepared in ployol shows higher cristallinity in comparison with that obtained by other ‘chimie douce’ methods.

Reduction under hydrogen of ferrite MFe2O4 (M: Fe, Co, Ni) nanoparticles obtained by hydrolysis in polyol medium: A novel route to elaborate CoFe2, Fe and Ni3Fe nanoparticles

A novel method to process metal and various alloy particles of nanometric size is described. The first step consists in the elaboration of MFe2O4 (M: Fe, Ni or Co) spinel nanoparticles in polyol medium via hydrolysis and the second one in gently reducing these latter under hydrogen at 300°C. X-ray diffraction analysis shows that pure Fe and CoFe2 alloy are well obtained by reducing Fe3O4 and CoFe2O4, respectively. This is not the case when we try to reduce NiFe2O4. A mixture of Fe and Ni3Fe is observed. TEM analysis reveals that the size of metal particles stays within the range of a few tenths of nm up to 150nm, while the precursors (MFe2O4) never exceed 5nm. Our results show that the formation of metal particles occurs via two main steps: (i) reduction of the spinel oxide nanoparticles into metal ones and (ii) aggregation of the latter, leading to larger metal nanoparticles. Magnetic measurements indicate that the as-obtained metallic materials have good magnetic properties mainly affected by the sizes of the nanoparticles and the purity of the reduced phases.

Layered nickel–cobalt hydroxyacetates and hydroxycarbonates: Chimie douce synthesis and structural features

Abstract Layered nickel–cobalt hydroxyacetates Ni 1− x Co x (OH) 2− y (OAc) y · n H 2 O were first prepared by hydrolysis in polyol medium and then layered nickel–cobalt hydroxycarbonates were obtained by solid/liquid exchange reaction starting from hydroxyacetates homologues. The interlamellar distances and the characteristics of IR absorption band of anions for low cobalt content hydroxyacetates ( x ≤0.25) are different from those with a higher cobalt amount. Such a difference is not observed for carbonate compounds. Despite these different features, UV analysis shows that cobalt (II) ions are present both in octahedral and tetrahedral sites for all acetate and carbonate compounds. The amount of cobalt in T d sites, inferred from magnetization measurements, increases up to 26–27% when the total amount of cobalt increases. Two structural models closely related to the hydrozincite one are proposed for the solid solutions. These models differ by the organization of anionic species and water molecules between the layers.

Influence of the synthesis parameters on the cationic distribution of ZnFe2O4 nanoparticles obtained by forced hydrolysis in polyol medium

Nanocrystals of ZnFe2O4 have been prepared by forced hydrolysis in polyols. Monodisperse, quasi-isotropic, highly crystalline, chemically homogeneous particles have been obtained as single crystals in the nanometer size range or as polycrystals in the submicrometer range depending on the nature of the polyol and the amount of water added. As inferred from EXAFS and XMCD data, the cation distribution in tetrahedral A (Td) and octahedral B (Oh) sites differs from that of bulk material, Fe3+ in A sites being observed in a ratio which depends on the crystallite size.

Layered nickel hydroxide salts: synthesis, characterization and magnetic behaviour in relation to the basal spacing

Layered nickel hydroxide salts Ni(OH)2−x(A)x·nH2O (A = NO3−, n-alkylsulfonates CnH2n+1SO3− with n = 10, 14, 18) have been prepared by exchange reaction in aqueous medium at pH = 8.5, starting from the layered hydroxide acetate Ni(OH)1.5(CH3COO)0.5·nH2O. This parent compound has been synthesized by hydrolysis in polyol medium. The obtained compounds present the typical features of the brucite-like structure with turbostratic disorder and an interlayer spacing varying in the range 7.5–32 Å. The magnetic properties have been investigated by means of dc and ac measurements. Two main interactions are found in these materials. On one hand, ferromagnetic in-plane exchange interactions dominate at high temperature, as deduced from the positive Weiss constant, while interlayer ferromagnetic interactions of dipolar origin are responsible for the 3D order at low temperature. This order is indicated by the hysteresis loops below a critical temperature lying in the range 16–18 K. The magnetic properties will be discussed in relation to the structural features, and are mainly driven by the length of the intercalated anion and its head-group functionality. It will be shown that these compounds form a novel series of layered materials for which the model of ferromagnetic layers interacting through dipolar coupling can be successfully applied.

Metastable solid solutions in the system ZnOCoO: synthesis by hydrolysis in polyol medium and study of the morphological characteristics

Metastable solid solutions in the system ZnOCoO have been synthesized by hydrolysis of ionic zinc and/or cobalt salts in polyol medium. The solubility of Co in the zincite oxide was significantly increased (at.% Co=65) compared to that obtained under thermodynamical equilibrium (at.% Co=6.5 at 800°C). CoO was also obtained via this route. The products are made up of sub-micrometer particles. A detailed study of their morphology along with pure ZnO particle morphology was conducted. Different growth mechanisms are evidenced.

Layered Hydroxide Metal Acetates (Metal = Zinc, Cobalt, and Nickel): Elaboration via Hydrolysis in Polyol Medium and Comparative Study

Layered hydroxide metal acetates (metal = zinc, cobalt, and nickel) have been prepared by a new route belonging to the chimie douce method. This novel method involves the hydrolysis, in polyol medium, of in situ-formed complexes supposed to be alkoxyacetates. These layered hydroxide metal acetates present poorly ordered character, and their X-ray patterns have features typical of lamellar compounds with turbostratic disorder. Their chemical formula was established to be M(OH)2-x(CH3COO)x·nH2O with (x, n) = (0.42, 0.31), (0.38, 0.53), and (0.40, 0.63) for Zn, Co, and Ni, respectively. The layered hydroxide nickel acetate has a classical brucite structure with a random substitution of some hydroxyl groups by acetate groups. The layered hydroxide zinc and cobalt acetates are isomorphous with the hydrozincite structure, in which cations are located in both octahedral and tetrahedral sites. The acetate anion behaves as a unidentate ligand in LHS−Ni and LHS−Co, where LHS indicates layered hydroxide salt, and is intercalated as a free anion in the zinc compound. The dehydration is a reversible topotactic process for LHS−Ni and Co, whereas it is a destructive process in the case of LHS−Zn.