José M. Saniger

Synthesis of multi branched carbon nanotubes in porous anodic aluminum oxide template

Porous anodic aluminum oxide (AAO) templates, obtained by anodization of aluminum plates at relatively high voltages, were used for growing multi-branched carbon nanotubes which copy the three-dimensional branching structure of the nanochannels in the template. The formation of these branched nanochannels is characteristic of AAO templates grown at 60 V. When AAO templates are grown at 40 V or lower, straight channels and carbon nanotubes (CNTs) are obtained. At 60 V some ramifications grow for a short time from the main axis of the pore, following the direction of film growth. The repetition of this process along the main channel induces a kind of three-dimensional pore structure which is copied when the CNTs are grown in the template. In this way it is possible to get bundles of branched carbon nanotubes grown into AAO templates with a tailored ramified channel structure.

Characterization of anodic porous alumina by AFM

Abstract The topography of supported and unsupported anodic aluminum oxide (AAO) films was measured by AFM under different testing modes. The supported film, attached onto an aluminum substrate, is mechanically stable and the contact mode shows good resolution for imaging the intrinsic features of the surface. Additionally, the non-contact mode can detect the presence of adsorbed species on the surface, which are not detected by the contact mode. On the contrary, for the unsupported alumina film, the non-contact mode shows better resolution, even for surface pore detection. These results are discussed in view of the different mechanical properties of both types of alumina films, and the magnitude of the sample–tip interaction for each operation mode. In relation with the pore arrangement, a single-step anodization process results in a dense but non-regular pore pattern. Regular pore arrays was obtained with a two-step anodization method using both oxalic and sulfuric acid as oxidation agents. AFM characterization allows the evaluation of the order of the pore array, the pore density and the external shape of AAO films obtained under different experimental approaches. A reliable determination of the internal diameter and shape of the pores is not well accomplished under the present experimental conditions.

Electrically conducting polyaniline–poly(acrylic acid) blends

We report an electrically conducting polyaniline–poly(acrylic acid) blend coatings prepared by mixing the emeraldine base (EB) form of polyaniline (PANI) and poly(acrylic acid) (PAA) aqueous solution. The samples show a moderate electrical conductivity σ. If they are immersed in an HCl aqueous solution, the conductivity of the samples is increased by two or three orders of magnitude and their thermal stability is also improved. Optical transmittance spectra show a complete protonation of PANI–PAA blends after immersion in HCl aqueous solution. Fourier transform infrared spectroscopy studies indicate that the better thermal stability of σ could come from the more stable protonated imine nitrogen ions. A low percolation threshold phenomenon is observed in PANI–PAA blends, from a strong interaction between the carboxylic acid groups of PAA and the nitrogen atoms of PANI.

Thin films of polyaniline–polyacrylic acid composite by chemical bath deposition

Polyaniline (PANI)–polyacrylic acid (PAA) composite thin films were deposited at room temperature on glass and polymethyl methacrylate substrates by introducing these into a freshly prepared chemical bath of HCl, PAA, aniline monomers and (NH4)2S2O8. Compared to the single PANI films, which were obtained from the same bath constitution but without PAA solution, the composite films showed a red shift at the maximum optical transmittance peak and a slightly lower electrical conductivity. Fourier transform infrared spectroscopy studies of the PANI composite thin films indicated the presence of the acid-base reaction product between PANI and PAA, as well as PAA molecule incorporation in the films. Atomic force microscopy analysis also showed morphologic and mechanical elasticity differences between the single PANI film the composite films deposited by the chemical bath method.

Use of Recombinant Rotavirus VP6 Nanotubes as a Multifunctional Template for the Synthesis of Nanobiomaterials Functionalized With Metals

The structural characteristics and predefined constant size and shape of viral assemblies make them useful tools for nanobiotechnology, in particular as scaffolds for constructing highly organized novel nanomaterials. In this work it is shown for the first time that nanotubes formed by recombinant rotavirus VP6 protein can be used as scaffolds for the synthesis of hybrid nanocomposites. Rotavirus VP6 was produced by the insect cell‐baculovirus expression vector system. Nanotubes of several micrometers in length and various diameters in the nanometer range were functionalized with Ag, Au, Pt, and Pd through strong (sodium borohydride) or mild (sodium citrate) chemical reduction. The nanocomposites obtained were characterized by transmission electron microscopy (TEM), high‐resolution TEM (HRTEM) with energy dispersive spectroscopy (EDS), dynamic light scattering, and their characteristic plasmon resonance. The outer surface of VP6 nanotubes had intrinsic affinity to metal deposition that allowed in situ synthesis of nanoparticles. Furthermore, the use of preassembled recombinant protein structures resulted in highly ordered integrated materials. It was possible to obtain different extents and characteristics of the metal coverage by manipulating the reaction conditions. TEM revealed either a continuous coverage with an electrodense thin film when using sodium citrate as reductant or a discrete coverage with well‐dispersed metal nanoparticles of diameters between 2 and 9 nm when using sodium borohydride and short reaction times. At long reaction times and using sodium borohydride, the metal nanoparticles coalesced and resulted in a thick metal layer. HRTEM‐EDS confirmed the identity of the metal nanoparticles. Compared to other non‐recombinant viral scaffolds used until now, the recombinant VP6 nanotubes employed here have important advantages, including a longer axial dimension, a dynamic multifunctional hollow structure, and the possibility of producing them massively by a safe and efficient bioprocess. Such characteristics confer important potential applications in nanotechnology to the novel nanobiomaterials produced here. Biotechnol. Bioeng. 2009; 104: 871–881.

Partial fluorination of γ-alumina by gaseous fluorine

Abstract Pluorination of γ-alumina samples with 100 and 300 mbar of undiluted gaseous fluorine at room temperature, results in the incorporation of 3.0% (sample a ) and 6.7% in weight (sample b ) of fluorine, respectively. The fluorinated samples were studied by XRD and FT-IR. The X-ray diffractograms show no significant changes for sample a and the Formation of a second phase of aluminum hydroxyfluoride for sample b . Infrared spectra of the hydroxyl region show important modifications of the OH hands: for sample a , the removal of the OH groups of basic character can be observed, as well as the near disappearance of the hydrogen bond interaction among other OH groups; on the other hand, sample b presents a new strong and sharp band related to the OH groups of the aluminum hydroxyfluoride phase. The deconvolution analysis of the Al-O vibration region, for sample b , allows the identification of new bands associated with the aluminum hydroxyfluoride phase. The splting of the former Al-O bands of the γ-alumina is attributed to the loss of symmetry of the polyhedral AlO 4 and AlO 6 croups due to the O/F substitution.

Dealumination and surface fluorination of H-ZSM-5 by molecular fluorine

Abstract At room temperature, framework aluminum (FAl) is extracted rapidly from the lattice of H-ZMS-5 by molecular fluorine. Ionic fluoro-complexes containing octahedral aluminum are formed within the micropores of the zeolite. The structure remains intact while the Si/FAl increases, for instance from 27 to 233 or from 55.2 to 382. As shown previously, the behavior of HY with respect to molecular fluorine is similar. The terminal SiOH in H-ZSM-5 are also fluorinated. The extent of this reaction was negligible in the case of HY. The quantitative distinction between the fluorine atom in SiF and the aluminum fluoro-complexes is possible using 19 F MAS NMR, HETCOR and TRAPDOR. The good agreement between 27 Al and 19 F NMR data and the quantitative analysis of the infrared spectra in the OH stretching region is outlined. In particular, the disputed assignment of the 3700 cm−1 band to OH on non-framework aluminum moieties is elucidated.

Simulation of the infrared spectra of transition aluminas from direct measurement of Al coordination and molecular dynamics

Abstract A new way to interpret the infrared spectra of transition aluminas in the OH as well as in the AlO stretching spectral region is proposed. It takes into account the recent and key progresses made possible by different techniques of 27 Al high resolution NMR spectroscopy as well as by the application of molecular dynamics. The fundamental principle is the consideration of Al atom pairs. These Al atoms have all possible coordinations with respect to oxygen. A distinction between the bulk and surface phase’s contributions is possible. The predictive power of this new approach is emphasized.

Micro-facet solar concentrator

A low-cost micro-facet solar concentrator is proposed. A large number of small flat mirrors are situated in a parabolic surface to approximate a large parabolic mirror. Low-cost commercial flat mirrors can be used for manufacturing such concentrators. Geometrical analyses show that this concentrator will have a concentration rate of some hundreds of suns. The problems of production of micro mirrors, support components, and the automatic assembly of the concentrator are discussed. Rough estimations show that the cost of the concentrator should be ∼

Thermal spikes in Ag/Fe and Cu/Fe ion beam mixing

55 per square metre of concentrator surface.