Philippe Decorse

One-step UV-induced modification of cellulose fabrics by polypyrrole/silver nanocomposite films

Cellulose fabrics were coated with polypyrrole-silver (PPy/Ag) nanocomposite films via one pot photopolymerization in aqueous media. This process was optimized for various concentrations of pyrrole/textile weight ratios with fixed molar ratio of [pyrrole]/[AgNO(3)] as 2.5. Simple weight measurements of the fabrics indicated progressive coating of PPy/Ag versus initial pyrrole/fabric weight ratio and photopolymerization time. X-ray diffraction (XRD) data confirm the nano-size (10-30 nm) and metallic state of Ag crystallites. The metallic state of silver particles was also confirmed by X-ray photoelectron spectroscopy (XPS). We demonstrate that UV-induced polymerization of pyrrole in the presence of AgNO(3) is simple and fast compared to chemical oxidative polymerization in the absence of UV light. More importantly, it permits to coat cellulose fabrics in one pot by polypyrrole/Ag nanocomposites films in environmentally friendly aqueous solutions at room temperature.

Photocatalytic activity of TiO2 nanofibers sensitized with ZnS quantum dots

ZnS–TiO2 hetero-nanostructured photocatalysts were synthesized by the impregnation of ZnS quantum dots (QDs) on the surface of TiO2 nanofibers. Samples were characterized by X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEG-SEM), X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance spectroscopy. The photocatalytic activity of the prepared nanostructures was assessed by the photodegradation of methylene blue in an aqueous solution under UV irradiation. It was found that titanium dioxide impregnated with ZnS QDs increased photocatalytic activity. We demonstrated that methylene blue was more efficiently photodegraded by UV irradiation using ZnS-TiO2 heterogeneous photocatalysts than using pristine TiO2 nanofibers.

One step synthesis of highly ordered free standing flexible polypyrrole-silver nanocomposite films at air–water interface by photopolymerization

Free standing polypyrrole-silver nanocomposite films were prepared by interfacial photopolymerization of pyrrole (in DCM) using AgNO3 (aqueous) as photosensitizer. During the photopolymerization process, film formation starts first at the DCM–water interface and later at the air–water interface. The films prepared at the air–water interface are thin (<1 μm), flexible, having a very low content of uniformly distributed metallic Ag nanoparticles and exhibiting high electrical conductivity ∼14.8 S cm−1. The thick films (∼200 μm) prepared at the DCM–water interface are porous, mechanically weak, contain a very high amount of Ag micro and nanoparticles and exhibit two orders of magnitude lower conductivity ∼0.1 S cm−1. High conductivity of PPy-Ag films formed at the air–water interface is attributed to controlled polymerization due to the limited availability of pyrrole and Ag+ ions at this interface.

Electron transfer properties of a monolayer of hybrid polyoxometalates on silicon

As electroactive molecules, polyoxometalates (POMs) have potential in charge trapping or resistive molecular memories, yet scarcely investigated until very recently. Since charge–discharge processes as well as transport properties are dependent upon the organization of the thin layers, we chose to explore a covalent approach and we prepared a diazonium post-functionalized Keggin-type polyoxometalate [PW11O39{Ge(p-C6H4–CC–C6H4–N2+)}]3− that was subsequently anchored on hydrogenated n-type Si(100) surfaces. A flat and homogeneous hybrid POM monolayer is obtained and characterized by AFM, ellipsometry and XPS techniques. Vertical and lateral electron transfers are studied by cyclic voltammetry and scanning electrochemical microscopy (SECM). If the electron transfer between the POM layer and the silicon surface is quite slow (kETvert = 5 s−1), SECM suggests that the monolayer displays a good lateral conductivity. Interestingly, SECM experiments evidence the influence of the organization of the layer on the lateral charge transfer and show the possibility to accumulate negative charges within the POM monolayer.

Electrochemical investigation of free-standing polypyrrole–silver nanocomposite films: a substrate free electrode material for supercapacitors

We report a facile route for synthesis of free standing polypyrrole–silver (PPy–Ag) nanocomposite films by photopolymerization of pyrrole using AgNO3 as photosensitizer in aqueous medium. In this process PPy–Ag films were formed at the air–water interface and at the bottom of the beaker. The films formed at the air–water interface are thin (≤2 μm), flexible, have a uniform distribution of metallic Ag nanoparticles and exhibit electrical conductivity (∼1.5 S cm−1). The thick (∼200 μm) PPy–Ag films prepared at the bottom of the beaker exhibit lower conductivity (∼0.15 S cm−1). Interestingly, the more conductive thin PPy–Ag films exhibit a low specific capacitance of 58 F g−1 as compared to the specific capacitance of 282 F g−1 for the thicker PPy–Ag films at a 1 mV s−1 scan rate in 0.5 M K2SO4 electrolyte. The better electrochemical activity and high specific capacitance of the thicker PPy–Ag films is attributed to their porous structure, which provides a larger electrolyte accessible conductive surface for redox reactions. This simple approach for the synthesis of PPy–Ag films along with their promising electrochemical properties allows their possible application as a substrate free electrode material for supercapacitors.

Synergetic effect of CdS quantum dots and TiO2 nanofibers for photoelectrochemical hydrogen generation

In this work, we developed a new type of nanostructured photoanodes for photoelectrochemical water splitting. They are based on CdS–TiO2 nanocomposite films, supported on conductive Ti sheets, prepared by an easy-to-achieve three-step method. It involves the production of TiO2 nanofibers (NFs) using a controlled corrosion route of polished Ti sheets, the preparation of size-controlled CdS quantum dots (QDs) by the polyol process and the direct impregnation of TiO2/Ti sheets by QDs in suspension. The photoelectrochemical (PEC) properties of the resulting nanostructures were measured, using a homemade electrochemical cell illuminated with a standard Xenon lamp, and compared to those of bare TiO2 NFs. A net enhancement of the photocurrent was observed after CdS impregnation, suggesting a low carrier recombination rate and a higher efficiency of the PEC device for solar water splitting, as the induced photocurrent is related to the electrons needed to reduce H+ ions into H2 at the cathode electrode (Pt wire).

One-Step Formation of Bifunctionnal Aryl/Alkyl Grafted Films on Conducting Surfaces by the Reduction of Diazonium Salts in the Presence of Alkyl Iodides

The formation of partial perfluoroalkyl or alkyl radicals from partial perfluoroalkyl or alkyl iodides (ICH2CH2C6F13 and IC6H13) and their reaction with surfaces takes place at low driving force (∼-0.5 V/SCE) when the electrochemical reaction is performed in acetonitrile in the presence of diazonium salts (ArN2(+)), at a potential where the latter is reduced. By comparison to the direct grafting of ICH2CH2C6F13, this corresponds to a gain of ∼2.1 V in the case of 4-nitrobenzenediazonium. Such electrochemical reaction permits the modification of gold surfaces (and also carbon, iron, and copper) with mixed aryl-alkyl groups (Ar = 3-CH3-C6H4, 4-NO2-C6H4, and 4-Br-C6H4, R = C6H13 or (CH2)2-C6F13). These strongly bonded mixed layers are characterized by IRRAS, XPS, ToF-SIMS, ellipsometry, water contact angles, and cyclic voltammetry. The relative proportions of grafted aryl and alkyl groups can be varied along with the relative concentrations of diazonium and iodide components in the grafting solution. The formation of the films is assigned to the reaction of aryl and alkyl radicals on the surface and on the first grafted layer. The former is obtained from the electrochemical reduction of the diazonium salt; the latter results from the abstraction of an iodine atom by the aryl radical. The mechanism involved in the growth of the film provides an example of complex surface radical chemistry.

Visible-light photocatalytic performances of TiO2 nanobelts decorated with iron oxide nanocrystals

A TiO2–Fe2O3 hetero-nanostructure was fabricated via a three-step method and evaluated for its visible-light photocatalytic performances. TiO2 nanobelts (NBs) were synthesized by controlled hydrothermal oxidation of a Ti sheet while Fe2O3 nanocrystals (NCs) were prepared by forced hydrolysis in polyol. NBs were then decorated with NCs using direct impregnation. The structure, morphology and chemical composition of the resulting hybrids were investigated by X-ray Diffraction (XRD), Field Emission Gun Scanning Electron Microscopy (FEG-SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), Raman and UV-visible diffuse reflectance spectroscopy. The photocatalytic activity was assessed by following methylene blue photodegradation in an aqueous solution under visible light irradiation and comparing to that of bare TiO2 NBs. The photoelectrochemical properties were determined by measuring their ability to oxidize water under mimetic sunlight irradiation. The significant observed improvement was attributed to sensitization of the wide-gap titania semiconductor by the narrow-gap hematite one, namely faster interfacial charge transfer and wider spectral light absorption.

Functionalized magnetic nanoparticles for the decontamination of water polluted with cesium

Magnetic nanoparticles are attracting considerable interest because of their potential applications in practically all fields of science and technology, including the removal of heavy metals from contaminated waters. It is, therefore, of great importance to adapt the surfaces of these nanoparticles according to the application. In this work advanced nanoparticles (NPs) with well-tailored surface functionalities were synthesized using the polyol method. The efficiency of a chelating agent, succinyl-β-cyclodextrin (SBCD), was first investigated spectrophotometrically and by Isothermal Titration Calorimetry (ITC). SBCD was then grafted onto nanoparticles previously functionalized with 3-aminopropyl triethoxsilane (NP-APTES). The resulting NP-SBCD system was then incubated with a solution of cesium. After magnetic separation, the solid residue was removed from the supernatant and characterized by X-Ray Photoelectron spectrometry (XPS),X-Ray Fluorescence spectrometry (XRF) and Superconducting QUantum Interference Device(SQUID) magnetometry. These characterizations show the presence of cesium in the solid residue, which indicates Cs uptake by the NP-SBCD system. This nanohybrid system constitutes a promising model for heavy metal decontamination.

Powerful Surface Chemistry Approach for the Grafting of Alkyl Multilayers on Aluminum Nanoparticles.

The synthesis of aluminum nanoparticles (Alnp) has raised promising perspectives these past few years for applications in energetic materials. However, because of their high reactivity, it is crucial to functionalize them before their use. In this work, we propose an original and simple chemical approach to graft spontaneously alkyl layers derived from alkyl halides at the surface of Alnp, by relying on the highly reductive character of these nanoparticles, when they are in the unoxidized form. Alnp were prepared in a glovebox and reacted with alkyl halides (RI and RBr) to give modified Alnp-R, as shown by infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction, thermogravimetric analysis (TGA), and microscopy. The coating is made of alkyl multilayers, which were found to be strongly anchored at the Alnp surface, as it resisted 2 h of rinsing in toluene. An electrocatalytic electron transfer promoted by Alnp is proposed to describe the mechanism of this grafting reaction.