Patricia Beaunier

Conducting polymer nanostructures for photocatalysis under visible light

Visible-light-responsive photocatalysts can directly harvest energy from solar light, offering a desirable way to solve energy and environment issues. Here, we show that one-dimensional poly(diphenylbutadiyne) nanostructures synthesized by photopolymerization using a soft templating approach have high photocatalytic activity under visible light without the assistance of sacrificial reagents or precious metal co-catalysts. These polymer nanostructures are very stable even after repeated cycling. Transmission electron microscopy and nanoscale infrared characterizations reveal that the morphology and structure of the polymer nanostructures remain unchanged after many photocatalytic cycles. These stable and cheap polymer nanofibres are easy to process and can be reused without appreciable loss of activity. Our findings may help the development of semiconducting-based polymers for applications in self-cleaning surfaces, hydrogen generation and photovoltaics.

One-step construction of silver nanowires in hexagonal mesoporous silica using the polyol process

An original one-step preparation of single-crystal silver nanowires in hexagonal mesoporous silica is presented. The silver precursor, silver nitrate, is reduced in ethylene glycol (EG). This procedure avoids thermal treatments which can lead to phase segregation. The absorbance spectrum of the resulting hybrid material exhibits a transverse resonance plasmon peak near 360 nm whereas the longitudinal oscillation is shifted to the near-infrared region at about 1500 nm.

Modification of TiO2 by Bimetallic Au-Cu Nanoparticles for Wastewater Treatment

Au, Cu and bimetallic Au-Cu nanoparticles were synthesized on the surface of commercial TiO2 compounds (P25) by reduction of the metal precursors with tetrakis (hydroxymethyl) phosphonium chloride (THPC) (0.5 % in weight). The alloyed structure of Au-Cu NPs was confirmed by HAADF-STEM, EDS, HRTEM and XPS techniques. The photocatalytic properties of the modified TiO2 have been studied for phenol photodegradation in aqueous suspensions under UV-visible irradiation. The modification by the metal nanoparticles induces an increase in the photocatalytic activity. The highest photocatalytic activity is obtained with Au-Cu/TiO2 (Au/Cu 1:3). Their electronic properties have been studied by time resolved microwave conductivity (TRMC) to follow the charge-carrier dynamics. TRMC measurements show that the TiO2 modification with Au, Cu and Au-Cu nanoparticles plays a role in charge-carrier separations increasing the activity under UV-light. Indeed, the metal nanoparticles act as a sink for electron, decreasing the charge carrier recombination. The TRMC measurements show also that the bimetallic Au-Cu nanoparticles are more efficient in electron scavenging than the monometallic Au and Cu ones.

TiO2-supported Rh nanoparticles: From green catalyst preparation to application in arene hydrogenation in neat water

TiO2-supported Rh(0) nanoparticles were prepared by an easy method under mild conditions in neat water. They proved to be highly active catalysts for arene hydrogenation in water with TOFs up to 33 333 h−1.

Using inorganic silicate precursor/molybdenum peroxo complexes/onium salt interfaces in aqueous acidic media to design mesoporous silica with high molybdenum content and high dispersion

Mesoporous molybdosilicate, [Mo]-MCM-41, molecular sieves with variable amounts of molybdenum ( VI ) have been synthesized in acidic media from MoO 3 , aqueous hydrogen peroxide and tetraethyl orthosilicate as the silicon source. This procedure avoids the formation of iso-(or hetero-)polyooxometalates and eliminates the need for careful control of the rate of hydrolysis of the metal precursors, e.g. alkoxides, sometimes involved in the syntheses of transition metal-containing mesoporous materials. The parent materials are calcined in air (60° Ch ’1, isothermal at 920 K for 4 h) to decompose the organic structure-directing agent. The materials have been characterized by chemical analysis, X-ray diVraction and EDS analysis, TEM, 29Si MAS NMR, UV-visible diVuse reflectance spectroscopy and nitrogen sorption isotherms. In contrast to previous preparations, such syntheses give an increase in the Mo/Si (mol/mol ) ratio of up to 0.04 and a greater dispersion of the surface species. For chemical characterization, (R)-(+)limonene epoxidation with anhydrous tert-butylhydroperoxide/decane/pentane mixtures was used as a test; high conversions and selectivities can be obtained at 20°C. DiVerent leaching behaviors were observed as a consequence of the diVerent catalyst preparation methods. A comparative IR spectroscopic study was performed to obtain evidence for the formation of [Mo]-OOt-Bu surface species.

PEDOT nanostructures synthesized in hexagonal mesophases

We describe a single step preparation of nanostructures of poly(3,4-ethylenedioxythiophene), PEDOT, in the hydrophobic domains of cationic surfactant-based hexagonal mesophases via chemical oxidative polymerization of EDOT monomers using FeCl3 as an oxidizing agent. After polymerization, the hexagonal structure of the mesophases is preserved as demonstrated by polarized light microscopy and X-ray scattering measurements. After extraction from mesophases, the chemical structure of PEDOT is confirmed by Fourier transform infrared spectroscopy. Moreover, PEDOT morphology is checked by transmission and scanning electron microscopies. PEDOT nanostructures with spindle-like or vesicle-like shapes are obtained depending on the experimental conditions. In the original method, high resolution atomic force microscopy, coupled with infrared nanospectroscopy, is used to probe the local chemical composition of PEDOT nanostructures. Finally, the as-prepared PEDOT polymers are characterized by both good thermal stability up to 200 °C and a relatively high conductivity value up to 0.4 S cm−1 as determined by thermogravimetric analysis and four probe measurements respectively.

Facile synthesis of Pd nanostructures in hexagonal mesophases as a promising electrocatalyst for ethanol oxidation

One of the significant challenges for the commercialization of direct ethanol fuel cells (DEFCs) is the preparation of active, robust, and low-cost catalysts. In this work, a facile and reproducible method is demonstrated for the synthesis of Pd assembled nanostructures in a hexagonal mesophase formed by a quaternary system (Pd-doped water, surfactant, oil, and cosurfactant) via photoirradiation. The formation of Pd nanostructures in the confined region of hexagonal mesophases was further supported by water relaxation dynamics study using a solvation probe. The mesophases can be doped with high concentrations of a palladium salt (0.1 M) without any disturbance to the structure of the mesophases which results in a high yield and facilitates the clean synthesis of Pd nanostructures without using any toxic chemicals. Electrochemical measurement confirms that the as-prepared catalysts exhibit significant electrocatalytic activity for ethanol oxidation in alkaline solution. Additionally, we present an alternative strategy using reduced graphene oxide nanosheets in combination with Nafion (a proton conducting phase) as a support, revealing the pronounced impact on dramatically enhanced electrocatalytic activity and stability of Pd nanostructures compared to Nafion alone. This unique combination allowed the effective dispersion of the Pd nanostructures that is responsible for the enhancement of the catalytic activity. Our approach paves the way towards the rational design of practically relevant catalysts with both enhanced activity and durability for fuel cell applications.

Comparison of conventional and solid-state ion exchange procedures for the incorporation of lanthanum in H-beta zeolite

Abstract Lanthanum-exchanged beta zeolites have been prepared by a solid-state ion-exchange procedure which consists of calcining in static conditions a mechanical mixture of LaCl 3 .7H 2 O and H-beta zeolite. The exchanged samples have been characterized at various steps of their preparation by XRD, BET, FTIR, TEM, EDS and chemical analyses. The results have been compared to those obtained on samples exchanged in solution. In the case of conventional ion exchange in solution, the incorporation of La into the zeolitic pores is strongly limited due to the steric hindrance caused by the large hydration sphere of the La 3+ ions. As a consequence, strongly heterogeneous samples contaminated by La-rich crystalline particles are obtained even at rather low La contents or after repeating the exchange several times. In contrast, the yield for lanthanum incorporation reaches values as high as 100% when the solid-state exchange procedure is used. Moreover, the samples are highly homogeneous and no loss of crystallinity is observed in spite of the very simple conditions used (calcination in static). The exchange by La species of protons initially present in the H-beta parent sample is confirmed by FTIR spectra of OH groups, which also reveal that part of the incorporated La species interact with the silanol groups.

A surfactant-assisted preparation of well dispersed rhodium nanoparticles within the mesopores of AlSBA-15: characterization and use in catalysis

Well dispersed and efficient Rh(0) hydrogenation catalysts were obtained by the reduction of Rh(III)-exchanged mesoporous aluminosilicates by sodium borohydride in the presence of N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl) ammonium chloride.

Highly porous and monodisperse magnetic silica beads prepared by a green templating method

We describe the preparation of magnetic silica nanocomposite millimetric beads using alginate as a green biopolymer template. The simple and soft method which is used here is particularly suitable since the alginate template allows a multiscale control of the structure of the material, both its morphological characteristics at the millimetric scale and its porosity at the nanometric level. These nanocomposites are characterised by a high monodispersity, a perfect spherical shape, a very large and multiscale porosity with pore diameters ranging from 2 nm to more than 50 nm, a homogeneous dispersion of the magnetic nanoparticles in the silica matrix and a high magnetic susceptibility which increases linearly with the volume fraction of the nanoparticles. These highly porous materials which can be used as magnetic adsorbents in water treatment, showed a good sorption capacity for methylene blue, chosen as a model dye.