Oscar Giraldo

Materials: Spontaneous formation of inorganic helices

Attempts to generate films, wires, helices, rings and regular patterns out of inorganic materials have been going on for the past 100 years. We show here that stable helices of porous manganese oxide materials can be formed spontaneously from uniform sols and that they are excellent semiconductors. These inorganic helices contain micropores, can be converted into other structures, and their composition can be varied.

Analysis of a reactive extraction process for biodiesel production using a lipase immobilized on magnetic nanostructures

Magnetic nanoparticles were prepared by coprecipitating Fe(2+) and Fe(3+) ions in a sodium hydroxide solution and used as support for lipase. The lipase-coated particles were applied in a reactive extraction process that allowed separation of the products formed during transesterification. Kinetics data for triolein and ethanol consumption during biodiesel (ethyl oleate) synthesis together with a thermodynamic phase equilibrium model (liquid-liquid) were used for simulation of batch and continuous processes. The analysis demonstrated the possibility of applying this biocatalytic system in the reactive zone using external magnetic fields. This approach implies new advantages in efficient location and use of lipases in column reactors for producing biodiesel.

Simple route for the synthesis of copper hydroxy salts

No presente trabalho e apresentada uma nova e rapida rota de sintese em escala de laboratorio de hidroxinitrato de cobre(II), Cu2(OH)3NO3, mediante reacao de hidroxido de magnesio com solucao aquosa de nitrato de cobre(II). O material foi caracterizado por difratometria de raios X (estrutura monoclinica), absorcao atomica, espectroscopia vibracional (infravermelho com transformada de Fourier e Raman), analise termica e microscopia eletronica de varredura com EDX.

Palladium nanoparticles supported on layered hydroxide salts and their use in carbon-carbon coupling organic reactions

Palladium nanoparticles supported on zinc hydroxide salts were prepared by intercalation of [PdCl6]2- and its further reduction with ethanol under reflux. All the materials were completely characterized by atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), thermogravimetric/derivative thermogravimetric (TG/DTG) analyses, scanning electron microscopy (SEM), UV-Visible spectrometry and transmission electron microscopy (TEM). TEM analysis confirmed that the palladium nanoparticles were properly supported. The material containing supported palladium nanoparticles was used to promote Heck and Suzuki coupling reactions starting from aryl halides, with isolated yields of 98, 75 and 62% of biphenyl, cinnamic acid and 3-nitrobiphenyl, respectively.

Structural Analysis and Conduction Mechanisms in Polycrystalline Zinc Hydroxide Nitrate

The conduction and dielectric properties in zinc hydroxide nitrate (Z5HN) were studied in detail as a function of the temperature and relative humidity by impedance spectroscopy, and the structure was investigated by X-ray diffraction (XRD). Elemental analysis indicated a layered material containing carbonate anions [Zn5(OH)8(NO3)1.6(CO3)0.2·1.7H2O] due to the high capability of adsorption of Z5HN, which makes this material appropriate for applications in real conditions. The water content affected the interlayer distance, conductivity, and dielectric response of the layered material. An electrostatic repulsive interaction after reduction of the water content as a function of the temperature causes an increase of the interlayer distance and a decrease in the conductivity response and dielectric behavior. The highest conductivity, 10-7 Ω-1 cm-1, was obtained at a shorter interlayer distance for the sample heat-treated at 25 °C. The Z5HN synthesized was also characterized at different temperatures using thermogravimetric analysis and Fourier transform infrared and Raman spectroscopy. Multipeak analysis of the XRD patterns at various relative humidity levels showed the formation of a most hydrated phase and an increase of the interlayer distance related with the adsorption of water molecules. This layered material presented a conductivity of 10-5 Ω-1 cm-1 at high relative humidity (92%). The dipole-dipole interaction appeared to be the dominant mechanism for the dielectric behavior at the lowest temperatures and highest humidity due to the high water content in the Z5HN structure. Taking into account its crystallization water and high adsorption of water molecules in the interlayer region, a conduction pathway in the Z5HN structure was proposed, which provides the route for proton transport by hydrogen-bonding networks on the basis of a Grotthuss-type mechanism in facilitating the long-range proton hopping at 25 °C. The results for high relative humidity imply that a vehicular conduction mechanism also may contribute to the electrical response.