Rita C. G. Vinhas

Mechanisms of polymer film deposition from r.f. discharges of acetylene, nitrogen and helium mixtures☆

Mixtures of C2H2, He and N2 were polymerized in an r.f. discharge. Quantitative optical emission spectroscopy was used to determine relative concentrations of the key species CH and CN in the plasma as a function of the proportions of monomer gases in the feed, and to delineate the behavior of the electron mean energy and number density in the discharge. Transmission IR spectroscopy (IRS) and electron spectroscopy for chemical analysis (ESCA) of films deposited from discharges containing different proportions of nitrogen revealed the incorporation of both CH and CN in the deposited material. Deposition rates were also determined and their connection with deposition mechanisms via gas-phase and surface reactions is outlined.

SiO2/SnO2/Sb2O5 microporous ceramic material for immobilization of Meldola's blue: application as an electrochemical sensor for NADH.

The mixed oxide SiO(2)/SnO(2), containing 25 wt% of SnO(2), determined by X-ray fluorescence, was prepared by the sol-gel method and the porous matrix obtained was then grafted with Sb (V), resulting the solid designated as (SiSnSb). XPS indicated 0.7% of Sb atoms on the surface. Sb grafted on the surface contains Brønsted acid centers (SbOH groups) that can immobilize Meldolas blue (MB(+)) cationic dye onto the surface by an ion exchange reaction, resulting the solid designated as (SiSnSb/MB). In the present case a surface concentration of MB(+)=2.5×10(-11) mol cm(2) on the surface was obtained. A homogeneous mixture of the SiSnSb/MB with ultra pure graphite (99.99%) was pressed in disk format and used to fabricate a working electrode that displayed an excellent specific electrocatalytic response to NADH oxidation, with a formal potential of -0.05 V at pH 7.3. The electrochemical properties of the resulting electrode were investigated thoroughly with cyclic voltammetric and chronoamperometry techniques. The proposed sensor showed a good linear response range for NADH concentrations between 8×10(-5) and 9.0×10(-4) mol L(-1), with a detection limit of 1.5×10(-7) mol L(-1). The presence of dopamine and ascorbic acid did not show any interference in the detection of NADH on this modified electrode surface.

Vanadium oxide intercalated with polyelectrolytes: Novel layered hybrids with anion exchange properties

Novel anion exchange hybrid materials were developed by the insertion of poly(diallymethylammonium chloride) (PDDACl) and poly(allylamine hydrochloride) (PAHCl) polyelectrolytes into V(2)O(5) interlayer spaces using hydrothermal treatment and were used to host an anionic cyanine dye. A systematic study of the hybrid material synthesis by direct in situ reaction of PDDACl and PAHCl polycations with V(2)O(5) powders showed that the interlayer space of V(2)O(5) expands from 0.44 nm to 1.40 nm and 1.80 nm upon intercalation of PDDACl and PAHCl polyelectrolytes, respectively. X-ray photoelectron spectroscopy and DR UV-Vis-NIR spectroscopy revealed that some V(5+) sites were reduced to V(4+) during the intercalation of the polyelectrolytes, these acted as both charge balancing entities for the negative oxide sheets and carriers for exchange sites located in the V(2)O(5) interlayer space. The interlayer separation is consistent with the existence of coiled conformation of the polycations. The hybrid materials produced [PDDACl](0.24)[PDDA](0.29)V(2)O(5) and [PAHCl](0.28)[PAH](0.47)V(2)O(5), exhibited approximately 45.0% and 37.0% of chloride ions still available for anionic exchange, respectively. These materials were used to encapsulate a cyanine anionic dye. The presence of the dye was evidenced in the [PDDACl](0.24)[PDDA](0.29)V(2)O(5) by significant fluorescence, with emission peak centered at 617 nm.

Aluminium-magadiite: from crystallization studies to a multifunctional material

The synthesis of [Al]-magadiite (Si/Al = 15) was monitored during preparation and crystallization by the Aluminium-Induced Crystallization method developed previously (G. B. Superti, E. C. Oliveira, H. O. Pastore, G. Gatti and L. Marchese, Chem. Mater., 2007, 19, 4300–4315.). For monitoring purposes samples were collected at 0, 12 and 24 h and after aluminium introduction at 0, 6 and 12 h of hydrothermal treatment. A systematic study of the physicochemical and thermal properties of the products obtained at each step in [Al]-magadiite synthesis was performed by combining different experimental techniques [infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and solid-state magic-angle spinning nuclear magnetic resonance (MAS-NMR)]. 27Al MAS NMR confirmed the insertion of Al ions into the magadiite framework in tetrahedral positions. The results obtained showed that the hydrothermal treatment before aluminium insertion served essentially for the creation of magadiite seeds. Thus, induced crystallization by introduction of magadiite seeds directly in the synthesis gel showed that the synthesis duration could be reduced and variable Si/Al ratios showed that the increase in aluminium concentration affects the crystallinity of the material and allows us to obtain [Al]-magadiite with different Si/Al ratios in a single step. Different Altd nonequivalent sites were detected by 3QMAS-NMR experiment. X-Ray photoelectron spectroscopy (XPS) allowed designing the [Al]-magadiite structure as a pure silicon magadiite core with a thin layer of aluminosilicate deposited on top of it.

Ag Nanoparticles-Based Zinc Hydroxide-Layered Hybrids as Novel and Efficient Catalysts for Reduction of 4-Nitrophenol to 4-Aminophenol

Silver nanoparticles and zinc hydroxide-layered hybrid materials (AgNPs/ZHL) have been successfully developed as efficient catalysts for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with sodium borohydride. A facile and rapid visible-light assisted green route was used for the deposition of silver nanoparticles (AgNPs) on the external surface of ZHL material. The resulting AgNPs/ZHL hybrids contained AgNPs with spherical morphology and uniform size distribution. Moreover, the AgNPs/ZHL compounds exhibited excellent catalytic performance (the reduction reaction was finished within 4 min) and reusability (three cycles) toward the reduction of 4-NP to 4-AP in presence of sodium borohydride. The reduction reaction obeyed the pseudo-first-order kinetics. The rate constants increased with the increase of amount of the AgNPs deposited into the hybrid materials. These results suggest that the as-prepared catalysts (AgNPs/ZHL) have great potential for heterogeneous catalytic applications.

CARACTERIZAÇAO POR XPS DE CATALISADORES DE ÔXIDOS DE Al E Zn

As razoes atomicas Al/Al+Zn e S/Al+Zn para catalisadores de oxidos de Al e Zn, obtidos por coprecipitacao a partir dos sulfatos metalicos, sao determinadas por XPS (espectroscopia de fotoeletrons excitados por raio-X). Esses teores sao comparados aos obtidos por analise quimica e correlacionados com dados de ensaio catalitico da conversao do etanol em butadieno.