Ultrathin Polycrystalline Hematite and Goethite−Hematite Core−Shell Nanorods

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Oxygen reduction of pre-synthesized organically capped platinum nanoparticles assembled in mixed Langmuir–Blodgett films: Evolutions with the platinum amount and leveling after fatty acid removal

Mixed Langmuir–Blodgett (LB) films based on crown derivatized platinum nanoparticles (NPs) and fatty acid showed a direct electrochemical activity toward oxygen reduction reaction (ORR) in acidic medium. This paper reports on the original and strong effects observed in the electrochemical response of these two-phase systems towards oxygen reduction by varying the Pt amount in the mixed LB films. The easy manipulation of pre-synthesized organically capped nanoparticles, combined with the features of the Langmuir–Blodgett technique allows good control of the platinum loading in the films. Pt loadings are set by changing the number of deposited monolayers and/or their nanoparticle density. Loading variations induce strong modifications in the voltammograms and are considered in terms of the relative weight of the two phases: platinum nanoparticles and fatty acids. We point out the strong influence of the environment of platinum nanoparticles towards their electrocatalytical behaviour. Various effects, such as electrical resistance of the nanostructures are considered. Evolution of the peak current density ratios from O2 and [Fe(CN)6]3−/4− probes as a function of platinum loading in mixed films could suggest a possible change in the dominating number of electrons exchanged in the ORR. The effect of the fatty acid phase is definitely demonstrated by the leveling of the electrochemical responses after its elimination from the thin film structures. The electrochemical response is then likely governed by only the organic crown of the particles, which controls the ultimate local environment of the platinum particles. In such a situation, the optimized platinum loading is found to be 2.4 μg cm−2

Nanocomposite Langmuir–Blodgett films based on crown derivatized platinum nanoparticles: Synthesis, characterization, and electrical properties

International audienceThis paper deals with the crown derivatization of 4-mercaptoaniline functionalized platinum formation and the use of the resulting nanoparticles to build up controlled Langmuir and Langmuir–Blodgett films. It is shown that the high density of amine functions at the surface of platinum nanoparticles functionalized by 4-mercaptoaniline offers the possibility of over grafting with various molecules giving rise to different rate of crown derivatization ranging from 19% to 45%. The derivatizations process of the organic coating has been characterized by infrared spectroscopy and thermo gravimetric analysis. The elaboration of Langmuir and Langmuir–Blodgett films containing different ratio of derivatized nanoparticles and fatty acid is reported and the thin films are characterized using X-ray photoelectron spectroscopy and small-angle X-ray scattering. A marked structural anisotropy due to the deposition process is revealed, that corresponds in some cases to a well-defined layered organisation. Modifications in electrical conductivity induced by crown derivatization are reported. These crown derivatized particles are currently studied towards the oxygen reduction reaction