Nanocasting Synthesis of Ultrafine WO3 Nanoparticles for Gas Sensing Applications

Ultrafine WO3 nanoparticles were synthesized by nanocasting route, using mesoporous SiO2 as a template. BET measurements showed a specific surface area of 700 m 2/gr for synthesized SiO2, while after impregnation and template removal, this area was reduced to 43 m 2/gr for WO3 nanoparticles. HRTEM results showed single crystalline nanoparticles with average particle size of about 5 nm possessing a monoclinic structure, which is the favorite crystal structure for gas sensing applications. Gas sensor was fabricated by deposition of WO3 nanoparticles between electrodes via low frequency AC electrophoretic deposition. Gas sensing measurements showed that this material has a high sensitivity to very low concentrations of NO2 at 250°C and 300°C

Templated synthesis of mesoporous superparamagnetic polymers

We present a novel synthetic strategy for fabricating superparamagnetic nanoparticles randomly dispersed in a mesoporous polymeric matrix. This method is based on the use of mesoporous silica materials as templates. The procedure used to obtain these mesoporous magnetic polymers consisted in: a) generating iron oxide ferrite magnetic nanoparticles (FMNP) of size - 7-8 nm within the pores of the silica, b) loading the porosity of the silica/FMNP composite with a polymer (Polydivinylbenzene), c) selectively removing the silica framework from the resulting silica/FMNP/polymer composite. Such magnetic porous polymeric materials exhibit large surface areas (up to 630 m2g-1), high pore volumes (up to 0.73 cm3 g-1) and a porosity made up of mesopores. In this way, it is possible to obtain superparamagnetic mesoporous hybrid nanocomposites that are easily manipulated by an external magnetic field and display different magnetic behaviours depending on the textural properties of the template employed. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.Peer Reviewe

Signatures of clustering in superparamagnetic colloidal nanocomposites of an inorganic and hybrid nature

The individual and co-operative properties of inorganic and hybrid superparamagnetic colloidal nanocomposites that satisfy all the requirements of magnetic carriers in the biosciences and/or catalysis fields are been studied. Essential to the success of this study is the selection of suitable synthetic routes (aerosol and nanocasting) that allow the preparation of materials with different matrix characteristics (carbon, silica, and polymers with controlled porosity). These materials present magnetic properties that depend on the average particle size and the degree of polydispersity. Finally, the analysis of the co-operative behavior of samples allows for the detection of signatures of clustering, which are closely related to the textural characteristics of samples and the methodology used to produce the magnetic carriers. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.Peer Reviewe

Understanding Gas-Induced Structural Deformation of ZIF-8

International audienc

Direct synthesis of graphitic carbon nanostructures from saccharides and their use as electrocatalytic supports

An easy method is described for fabricating graphitic carbon nanostructures (GCNs) from a variety of saccharides; i.e., a monosaccharide (glucose), a disaccharide (sucrose) and a polysaccharide (starch). The synthesis scheme consists of: (a) impregnation of saccharide with Ni or Fe nitrates, (b) heat treatment under inert atmosphere (N2) up to 900°C or 1000°C and (c) oxidation in liquid phase to selectively recover the graphitic carbon. This procedure leads to GCNs with a variety of morphologies: nanopipes nanocoils and nanocapsules. Such GCNs have a high crystallinity, as shown by TEM/SAED, XRD and Raman analysis. The GCNs were used as supports for platinum nanoparticles, which were well dispersed (Mean Pt size ~2–3 nm). Electrocatalysts thus prepared have electrocatalytic surface areas in the 70–95 m2 g−1 Pt range and exhibit high catalytic activities towards methanol electrooxidation.Financial support for this research work provided by the Spanish MCyT (MAT2005-00262, MAT2004-01479 and FEDER)

Solid-phase synthesis of graphitic carbon nanostructures from iron and cobalt gluconates and their utilization as electrocatalyst supports

We present a novel and facile synthesis methodology for obtaining graphitic carbon structures from Fe(II) and Co(II) gluconates. The formation of graphitic carbon can be carried out in only one step by means of heat treatment of these organic salts at a temperature of 900 °C or 1000 °C under inert atmosphere. This process consists of the following steps: (a) pyrolysis of the organic gluconate and its transformation to amorphous carbon, (b) conversion of Fe2+ and Co2+ ions to Fe2O3 and CoO and their subsequent reduction to metallic nanoparticles by the carbon and (c) conversion of a fraction of formed amorphous carbon to graphitic structures by Fe and Co nanoparticles that act as catalysts in the graphitization process. The removal of the amorphous carbon and metallic nanoparticles by means of oxidative treatment (KMnO4 in an acid solution) allows graphitic carbon nanostructures (GCNs) to be selectively recovered. The GCNs thus obtained (i.e. nanocapsules and nanopipes) have a high crystallinity as evidenced by TEM/SAED, XRD and Raman analysis. In addition, we used these GCNs as supports for platinum nanoparticles, which were well dispersed (mean Pt size ~2.5–3.2 nm). Most electrocatalysts prepared in this way have a high electrocatalytical surface area, up to 90 m2 g-1 Pt, and exhibit high catalytic activities toward methanol electrooxidation.The financial support for this research work provided by the Spanish MCyT (MAT2005-00262, MAT2004-01479 and FEDER) is gratefully acknowledged. M.S. acknowledges the assistance of the Spanish MCyT in awarding a FPU grant