Roberta Brayner

Nanodisks of Au and Ag produced by laser ablation in liquid environment

Abstract Ablation of Au and Ag targets in water by a Cu vapor laser generates Au and Ag sols. The metal nanoparticles obtained after evaporation are disk-shaped (diameter in the 20–60 nm range, thickness of few nanometers). Their formation is observed at laser fluence between 10 and 20 J / cm 2 . Both aqueous sols are characterized by well-resolved plasmon bands around 400 nm (Ag) and 520 nm (Au).

Niobium pentoxide prepared by soft chemical routes: morphology, structure, defects and quantum size effect

Niobium pentoxide (Nb2O5) is prepared by soft chemical routes (digestion either in ammonia or in hydrazine solutions) and is compared to a commercial sample. According to various characterization methods (XRD, HRTEM, DTA-TG, UV-visible diffuse reflectance, Raman and EPR spectroscopies), Nb2O5 shows particular bulk and surface properties. The phase transformation temperatures (amorphousu2006→u2006pseudo-hexagonal, pseudo-hexagonalu2006→u2006orthorhombic and orthorhombicu2006→u2006monoclinic) for the synthetic Nb2O5 are about 100–150u2006°C higher than for the commercial sample. The textural properties depend strongly on the preparation method. After calcination at 400u2006°C, the sample prepared in ammonia has a larger pore volume (0.22 cm3 g−1) and a better resistance to sintering at 600u2006°C. The preparation in hydrazine gives the following advantages only if the gel is sonically redispersed in ethanol: low particle size, narrow size distribution, and higher resistance to sintering (140 m2 g−1 at 600u2006°C). Preparation in ammonia or in hydrazine favors the formation of defects, characterized by a significant absorption in the visible range adjacent to the interband transition (3.4 eV, 360 nm). These defects, which disappear upon heating in oxygen, are identified as Nb4+ species and ionized oxygen vacancies as confirmed by EPR measurements. Finally, the nanoparticles obtained by sonication in ethanol (average particle size 4.5 nm) shows a significant band gap increase (from 3.4 eV to 4.2 eV) which is assigned to a quantum size effect.

Ecotoxicological effects of carbon nanotubes and cellulose nanofibers in Chlorella vulgaris.

BackgroundMWCNT and CNF are interesting NPs that possess great potential for applications in various fields such as water treatment, reinforcement materials and medical devices. However, the rapid dissemination of NPs can impact the environment and in the human health. Thus, the aim of this study was to evaluate the MWCNT and cotton CNF toxicological effects on freshwater green microalgae Chlorella vulgaris.ResultsExposure to MWCNT and cotton CNF led to reductions on algal growth and cell viability. NP exposure induced reactive oxygen species (ROS) production and a decreased of intracellular ATP levels. Addition of NPs further induced ultrastructural cell damage. MWCNTs penetrate the cell membrane and individual MWCNTs are seen in the cytoplasm while no evidence of cotton CNFs was found inside the cells. Cellular uptake of MWCNT was observed in algae cells cultured in BB medium, but cells cultured in Seine river water did not internalize MWCNTs.ConclusionsUnder the conditions tested, such results confirmed that exposure to MWCNTs and to cotton CNFs affects cell viability and algal growth.

Adhesion of façade coating colonisers, as mediated by physico-chemical properties.

Abstract The adhesion of Klebsormidium flaccidum, Stichococcus bacillaris and Chlorella cf. mirabilis, three strains of green microalgae isolated from biofilms on façade coatings were investigated in a parallel plate flow chamber. The model surfaces tested were glass slides, and −CH3 (mediated by octadecyltrichlorosilane [OTS] and hexamethyldisilazane [HMDZ] modification) and -NH2 (aminopropyltriethoxysilane [APS] modification) terminated self-assembled monolayers. Algal physicochemical properties were evaluated by the microbial adhesion to solvents (MATS) assay and by contact angle measurements. The model surfaces were characterised by X-ray photoelectron spectroscopy analysis and by contact angle measurements. Predicted adhesion trends were then compared to in vitro measurements. The adhesion strength of the three algal strains followed the trend: APS > OTS > HMDZ > glass. The adhesion process thus seemed to be mediated by hydrophobic and electrostatic interactions, and was shown to be influenced by the algal culture age and the initial contact time.

Preparation, characterization and reactivity of Pd/Nb2O5 catalysts in hexa-1,5-diene hydrogenation

Abstract Palladium/niobia catalysts are prepared by various methods involving either gas or liquid phase reduction. Although giving rise to average or low dispersion, the reduction of palladium precursors in a liquid medium (hydrazine or ethylene–glycol) appears to be a promising method since a low dispersion favors the activity in the hydrogenation of hexa-1,5-diene in liquid phase. The substitution of alumina by niobia improves the fractional selectivity and the yield of hex-1-ene in all cases. A very good global selectivity is also observed.

Preparation and characterization of high surface area niobia, ceria–niobia and ceria–zirconia

Abstract Niobia, zirconia, ceria–niobia and ceria–zirconia oxide nanoparticles are prepared by soft chemical routes and show valuable textural properties. The pore volume and specific surface area keep significant values even after calcination at 873xa0K. According to DRX and STEM-EDX measurements, solid solutions are obtained in the case of ceria–zirconia, whereas separate phases are identified in ceria–niobia; in the latter case, however, UV–Vis diffuse reflectance spectroscopy shows also the formation of defects (color centers) arising from a partial dissolution at the interface of the oxide phases.

Liquid-phase hydrogenation of hexadienes on metallic colloidal nanoparticles immobilized on supports via coordination capture by bifunctional organic molecules

Abstract Colloidal Pd, Ru and Pd–Cu are prepared in polyol solution (propane-1,2-diol) by either steric stabilization via poly( N -vinyl-2-pyrrolidone) (PVP) or electrostatic stabilization. The coordination capture is carried out with γ-mercaptopropyltriethoxysilane (γ-MPS) and 3-aminopropyltriethoxysilane (3-APS) previously grafted on the Nb 2 O 5 and Al 2 O 3 supports via the silane group. After interaction of the colloidal solutions with the grafted support, the immobilization yield is nearly 100% in the case of electrostatic stabilization but lower for steric stabilization. All catalysts present a very good global selectivity in the liquid-phase hydrogenation of hexa-1,5-diene (selectivity to hexenes). The PVP-protected samples present an initial induction time (30–50xa0min) due to the partial elimination of PVP by the solvent ( n -heptane). The activity and hex-1-ene productivity of immobilized Pd samples are higher than those of unsupported colloidal Pd and immobilized Ru. This promising method, which avoids direct metal–support interactions, offer new possibilities to control the shape, size and structure of metal nanosized particles in a colloidal form, without change upon heterogenation.

Algal polysaccharide capsule-templated growth of magnetic nanoparticles

Polysaccharidic alginate biopolymers have been used as templates for the controlled growth of magnetic nanoparticles. Ni2+ and Co2+ can used to form alginate gels as spherical capsules. UV-visible absorption spectroscopy allowed the investigation of the environment of the metal ions within the biopolymer network. Reduction under flowing H2/N2 led to the formation of Co and Ni nanoparticles as well as CoNi nanoalloys. Even at 350 °C, the organic matrix was partially preserved. XRD, TEM and XPS analyses were used to characterize particle structure, size and morphology. SQUID measurements indicated that all particles were ferromagnetic at 2 K. This work suggests that alginate provides a well-defined, chemically and thermally stable environment for the formation of nanoparticles, leading to magnetic nanocomposites.

Abatement of volatile organic compounds: oxidation of ethanal over niobium oxide-supported palladium-based catalysts

Abstract Niobium-supported palladium-based catalysts (Pd, Pd–Cu and Pd–Au) were employed in the oxidation of ethanal. The catalysts were prepared according to original methods by either multi-steps (anchoring of complexes, calcination and reduction) or one-step (photoassisted reduction) procedures. The oxidation of ethanal was carried out in gas phase in a dynamic-differential reactor at 300xa0°C at atmospheric pressure. The activity/selectivity of the catalysts depend on (i) the catalyst preparation; (ii) the presence of a second metal. Addition of Au or Cu decreases the catalysts deactivation and the best performance in total oxidation was obtained with Pd–Au/Nb2O5 prepared by photoassisted reduction. As shown by in situ IR spectroscopy of adsorbed CO, this peculiarity may be ascribed to Au→Pd electron donation, which prevents the surface oxidation of palladium particles.

The Polyol Process

Among the chemical, physical, or electrochemical processes generally used in particles production, the polyol-mediated synthesis of inorganic nanoparticles appears as an easy to carry out and versatile route. In this chapter, properties of polyols (α-diols and etherglycols) are first recalled in order to explain the versatility of this process. Guidelines which allow controlling the nucleation and growth steps in such media are then given in order to obtain particles with well-defined characteristics namely, a uniform shape, a mean size in the micron, submicron or nanometer range with a narrow size distribution, and a low degree of agglomeration. Examples of size tuning of ferromagnetic metals (Fe, Co, Ni, and their alloys) and noble metals are given as well as examples of shape control leading to 1D nanostructures with a particulate emphasis on the growth mechanism of silver nanorods or nanowires. Examples of polyol-mediated synthesis of oxide (spinel ferrites, Cu2O, ZnO) nanoparticles through hydrolysis reaction are also given. Throughout this chapter it is pointed out how the polyol process allows tuning the size and shape-dependent magnetic properties of ferromagnetic metal or spinel ferrite particles which may be used as advanced functional materials in various fields: high permeability composite materials, high density recording media, high temperature permanent magnets, and in biomedical applications such as magnetic resonance imaging, cancer treatment by hyperthermia, or targeted drug delivery