Demonstrative experiments about gold nanoparticles and nanofilms: an introduction to nanoscience

International audienceAn important task of the scientific community is to provide non-specialized audience with explanations about what is nanoscience. Such explanations can be given during public conferences, seminars in high schools or lab work organized with teachers. And very often, the use of an experimental illustration greatly helps to raise the interest and the curiosity of the public. The present article will describe how the authors have used five simple and visual experiments in chemistry and physics to progressively introduce different audiences into the fascination of nanoscience. One experiment is the synthesis of gold nanoparticles with the Turkevich method and shows the progressive appearance of the ruby-red colour of the nanometric gold particles. The second and third experiments describe the way for modulating their colour and how to include them into a polymer and form a ruby-red coloured plastic film. The fourth experiment shows that starting from these nanoparticles, it is possible to turn them back into a yellow golden film. The last experiment is based on the optical properties of ultra-thin gold films. Using the plasmon resonance, it is possible to demonstrate that gold change colours from yellow to orange and green when a white light beam is shone on the gold interface. These visual experiments cannot be fully interpreted in front of a large audience but serve for rising curiosity

Oxidation of Porphyrins in the Presence of Nucleophiles: From the Synthesis of Multisubstituted Porphyrins to the Electropolymerization of the Macrocycles

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Photocurrents at polarized liquid|liquid interfaces enhanced by a gold nanoparticle film

Photocurrent responses associated with the interfacial quenching of the photo-excited water-soluble zinc meso-tetra(4-carboxyphenyl)porphyrin (ZnTPPC) by ferrocene have been studied at a water|1,2-dichloroethane interface in the absence and in the presence of adsorbed gold nanoparticles. Upon addition of methanol, a mirror-like gold film is formed and an important enhancement of the photocurrent response can be observed. Intensity modulated photocurrent spectroscopy experiments (IMPS) have been performed, in order to deconvolute in the frequency domain the contribution from the competition between the recombination and the product separation arising after the electron transfer, and the attenuation associated with the resistance and interfacial capacitance (RCint) time constant of the cell

Interfacial Self-Assembly of Water-Soluble Cationic Porphyrins for the Reduction of Oxygen to Water

AN APPEAL FROM JUDGMENT ENTERED BY THE THIRD JUDICIAL DISTRICT COURT, SALT LAKE COUNTY, STATE OF UTAH, MURRAY DEPARTMENT, The Hon. Michael K. Burton, Judge Presiding (Trial Court Case No. 00-201-0956

Artificial Photosynthesis at Soft Interfaces

The concept of artificial photosynthesis at a polarised liquid membrane is presented. It includes two photosystems, one at each interface for the hydrogen and oxygen evolution respectively. Both reactions involve proton coupled electron transfer reactions, and some ultrafast steps at the photosensitization stage

Self-Assembled Molecular Rafts at Liquid|Liquid Interfaces for Four-Electron Oxygen Reduction

The self-assembly of the oppositely charged watersoluble porphyrins, cobalt tetramethylpyridinium porphyrin (CoTMPyP4+) and cobalt tetrasulphonatophenyl porphyrin (CoTPPS4−), at the interface with an organic solvent to form molecular “rafts”, provides an excellent catalyst to perform the interfacial four-electron reduction of oxygen by lipophilic electron donors such as tetrathiafulvalene (TTF). The catalytic activity and selectivity of the self-assembled catalyst toward the four-electron pathway was found to be as good as that of the Pacman type cofacial cobalt porphyrins. The assembly has been characterized by UV−visible spectroscopy, Surface Second Harmonic Generation, and Scanning Electron Microscopy. Density functional theory calculations confirm the possibility of formation of the catalytic CoTMPyP4+/ CoTPPS4− complex and its capability to bind oxygen

Assemblages hybrides porphyrines-polyoxométallates : étude électrochimique, photochimique et photocatalytique

Polyoxometalates (POMs) constitute a unique class of inorganic metal-oxygen clusters with a wide variety of properties. They have for example good advantages for applications in photocatalysis, particularly for the reduction of metallic cations. However, these compounds absorb principally in the UV spectral domain, requiring consequently a light activation in this spectral domain. The aim of this work has been to show the ability to use the catalytic properties of POMs in using the visible light, in combining POM with visible photosensitizers like porphyrins. Several hybrid porphyrin(s)-POM systems have been successively studied. First, we have investigated the photocatalytic properties of such systems in homogeneous media. For that, three kinds of assemblies based on different interactions, have been studied: electrostatic interactions, coordination interactions, and covalent bonds. Afterwards, the study has been extended to supported systems, in order to carry out heterogeneous catalysis. Two different approaches have been considered: multilayers systems and copolymers porphyrin-POM obtained by electropolymerization. All these systems have been the object of a thorough physical chemistry study, particularly by electrochemistry, photochemistry (systems in solution), atomic force microscopy (supported systems)... Photocatalytic tests have also been performed. As a first step, Ag(I) ions have been chosen as a model system for photoreduction. Silver nanoparticles with various sizes and shapes have been formed.Les polyoxométallates (POM) constituent une classe unique de clusters inorganiques du type métal-oxygène possédant des propriétés remarquables. Ils ont par exemple de bons atouts pour des applications en photocatalyse, notamment pour la réduction de cations métalliques, comme en témoignent les nombreux travaux présents dans la littérature. Néanmoins, un inconvénient majeur réside en le fait que cette famille de composés absorbe principalement dans l'UV, nécessitant par conséquent une activation lumineuse dans ce domaine spectral. L'objectif de ce travail de thèse a alors été de montrer qu'il est possible d'utiliser les propriétés catalytiques des POM tout en utilisant la lumière visible, en leur associant des photosensibilisateurs absorbant dans le domaine du visible. Le choix s'est porté sur des chromophores de type porphyrine. Plusieurs assemblages hybrides porphyrines-POM ont alors été étudiés successivement au cours de ce travail. Tout d'abord, nous avons voulu étudier les propriétés catalytiques de ce type de systèmes en milieu homogène. Pour cela, trois types d'assemblages porphyrine(s)-POM ont été envisagés, basés chacun sur des interactions ou liaisons de natures différentes : des interactions électrostatiques, des interactions de coordination, ou encore des liaisons covalentes. Puis nous avons souhaité étendre notre étude à des systèmes supportés, en vue d'applications en catalyse hétérogène. Dans ce but, deux types de systèmes supportés ont été étudiés : des systèmes multicouches basés sur des interactions électrostatiques et des copolymères porphyrine-POM obtenus par voie électrochimique. Tous ces systèmes développés ont fait l'objet d'une étude physico-chimique approfondie, notamment par électrochimie, photochimie (systèmes en solution), microscopie à force atomique (systèmes supportés... Concernant les études photocatalytiques, la plupart de ces systèmes ont fait l'objet de tests envers la photoréduction d'ions Ag(I), choisis dans un premier temps comme système modèle. Des nanoparticules d'argent de tailles et de formes variées ont ainsi été obtenues

SECM investigations of immobilized porphyrins films.

International audienceElectronic properties of electrogenerated Zn-porphyrin layers linked by an electroactive linker and immobilized on a semitransparent ITO electrode were investigated by steady-state SECM in unbiased conditions in view of the numerous possible applications of such surface. This SECM strategy took advantage of the variations of the charge transfer kinetics of the organic redox couple (the mediator used in SECM) on ITO surface with the standard potential of the mediator. After preliminary characterization of nonmodified ITO, analysis of the SECM approach curves recorded with a series of redox mediators allows the characterizations of both film permeability and charge transport inside the organic film in conditions close to a "real optoelectronic device". Two types of porphyrin films were considered. In the first one, the film was produced by electropolymerization of a modified zinc-β-octaethylporphyrin in which the bipyridinium pendant substituent is first introduced. The second type of film was prepared directly from an in situ electropolymerization method in which the Zn porphyrin is simply oxidized in the presence of 4,4'-bipyridine. Experiments show the occurrence of efficient charge transport inside both films after initial reduction of the electroactive linker. However, the first preparation method leads to films with stronger blocking character versus organic molecules and higher charge injection rates

Comparing plasmonic electrodes prepared by electron-beam lithography and electrochemical reduction of an Au (iii) salt: application in active plasmonic devices

International audienceThis work describes two different methods for obtaining electrodes covered with gold nanoparticles: electron-beam lithography and electroreduction of an Au (III) salt by chronoamperometry. Localized surface plasmon resonances of these different electrodes have been compared. In a second step, these plasmonic AuNP electrodes were covered with an ultrathin organic film of bisthienylbenzene which displays a reversible voltage-dependent switch between conducting and insulating states. The effect of this conductance switch on the plasmonic properties of the AuNPs has been studied

Nanostructured Mixed Layers of Organic Materials Obtained by Nanosphere Lithography and Electrochemical Reduction of Aryldiazonium Salts

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