Roberto Candal

Precipitation of copper(II) hydrous oxides and copper(II) basic salts

The precipitation of copper(II) hydrous oxides and basic salts from solutions that became homogeneously alkaline by forced hydrolysis of urea has been studied as a function of solution composition, ageing time and temperature. The time required for the onset of precipitation increased with the initial copper(II) concentration, [CuII]0. The precipitate was found to be amorphous copper hydroxide containing variable amounts of carbonate; at the highest [CuII]0, basic copper nitrate also precipitated. Upon further ageing of the systems, tenorite or malachite particles were formed at the expense of amorphous copper hydroxide; the nature of the final solid phase depended on [CuII]0. In the presence of added sulfate anions, brochantite particles were precipitated; in these cases precipitation took place earlier. All processes occurred at rates that were strongly dependent on temperature, although the sequence of events remained essentially the same.Thermodynamic and kinetic factors influencing the formation of all possible solid phases are discussed. It is shown that spherical monodispersed copper(II) hydrous oxide particles can be synthesized when these factors are taken into account adequately.

Influence of the methods of TiO2 incorporation in monolithic catalysts for the photocatalytic destruction of chlorinated hydrocarbons in gas phase

Abstract Three different methods of fixing titanium dioxide on a monolithic, natural magnesium silicate matrix, onto-the-wall extrusion, wash-coating and sol–gel, are compared. Photo-assisted oxidation tests with chlorinated hydrocarbons, trichloroethylene (TCE) alone and in mixtures with perchloroethylene (PCE) were carried out with the monolithic photocatalysts. Results show that the use of extruded titania monoliths provides significant advantages for best stability of anatase, porosity and resistance to loss of active phase due to erosion. Catalysts obtained by the sol–gel method maybe a good option for this application, but the coating method must still be improved.

TiO2 on magnesium silicate monolith: effects of different preparation techniques on the photocatalytic oxidation of chlorinated hydrocarbons

In this article, the comparative results of the photocatalytic oxidation of trichloroethylene (TCE) alone and a mixture of chlorinated hydrocarbons (trichloroethylene, perchloroethylene and chloroform) in gas phase, obtained with three different monolithic catalysts in a flat reactor frontally illuminated with a Xenon lamp are presented. The three catalysts incorporate titanium dioxide (TiO2) as active phase on a magnesium silicate support, by means of different procedures: (i) incorporation of commercial TiO2 powder into the silicate matrix (“massic monolith”); (ii) sol–gel coating of the silicate support; (iii) impregnation with a commercial TiO2 aqueous suspension of the same silicate support. In the first case, the massic monolith was made from a 50:50 w/w mixture of magnesium silicate and “Titafrance G5” TiO2 powder. In the second case, a magnesium silicate monolith was coated with several layers of an aqueous TiO2 sol prepared from hydrolysis and condensation of titanium tetra-isopropoxide (Ti(OC3H7)4) in excess of acidified water (acid catalysis). The third catalyst was prepared by impregnating the same silicate support with several layers of “Titafrance G5” TiO2 powder water suspension. All the catalysts were thermal treated under comparable conditions in order to fix the TiO2 active phase to the silicate support. Although the performance of the massic monolith was better than the sol–gel monolith, the latter is of great interest because this technique allows the chemical composition of the active films to be easily modified.

Improving the physical properties of starch using a new kind of water dispersible nano-hybrid reinforcement

Plasticized cassava starch matrix composites reinforced by a multi-wall carbon nanotube (MWCNT)-hercynite (FeAl2O4) nanomaterial were developed. The hybrid nanomaterial consists of FeAl2O4 nanoparticles anchored strongly to the surface of the MWCNT. This nano-hybrid filler shows an irregular geometry, which provides a strong mechanical interlocking with the matrix, and excellent stability in water, ensuring a good dispersion in the starch matrix. The composite containing 0.04wt.% of the nano-hybrid filler displays increments of 370% in the Youngs modulus, 138% in tensile strength and 350% in tensile toughness and a 70% decrease in water vapor permeability relative to the matrix material. All of these significant improvements are explained in terms of the nano-hybrid filler homogenous dispersion and its high affinity with both plasticizers, glycerol and water, which induces crystallization without deterioration of the tensile toughness.

Facile synthesis of cobalt ferrite nanotubes using bacterial nanocellulose as template

A facile method for the preparation of cobalt ferrite nanotubes by use of bacterial cellulose nanoribbons as a template is described. The proposed method relays on a simple coprecipitation operation, which is a technique extensively used for the synthesis of nanoparticles (either isolated or as aggregates) but not for the synthesis of nanotubes. The precursors employed in the synthesis are chlorides, and the procedure is carried out at low temperature (90 °C). By the method proposed a homogeneous distribution of cobalt ferrite nanotubes with an average diameter of 217 nm in the bacterial nanocellulose (BC) aerogel (3%) was obtained. The obtained nanotubes are formed by 26-102 nm cobalt ferrite clusters of cobalt ferrite nanoparticles with diameters in the 9-13 nm interval. The nanoparticles that form the nanotubes showed to have a certain crystalline disorder, which could be attributed in a greater extent to the small crystallite size, and, in a lesser extent, to microstrains existing in the crystalline lattice. The BC-templated-CoFe2O4 nanotubes exhibited magnetic behavior at room temperature. The magnetic properties showed to be influenced by a fraction of nanoparticles in superparamagnetic state.

Size effect of ZnO nanorods on physicochemical properties of plasticized starch composites

This work demonstrates that the size of ZnO nanorods (ZnONR) with similar aspect ratio determines several physicochemical and microbiological properties of thermoplastic starch composites (TPS/ZnONR) at a given concentration of ZnONRs. A combination of sol-gel and hydrothermal methods was developed to synthesize ZnONR with different sizes but similar aspect ratios. Starch composites containing 1wt.% of ZnONR were prepared by casting. Composites with smaller size nanorods (ZnONR-S) showed more efficiency in shielding UVA radiation and had a higher solubility and water vapor permeability than those with larger nanorods (ZnONR-L). Mechanical properties, biodegradability and antibacterial activity were also influenced by the size of the ZnONR. X-ray diffraction analysis showed that composites with ZnONR-S maintained the typical B-V type starch structure, intensifying the V-type starch structure peaks, while composite with ZnONR-L induced the formation of an amorphous structure, preventing starch retrogradation during storage. Properties affected by nanorods size are fundamental in determining composite applications.

Effect of O2+, H2++ O2+, and N2++ O2+ ion-beam irradiation on the field emission properties of carbon nanotubes

The effect of O2+, H2++ O2+, and N2++ O2+ ion-beam irradiation of carbon nanotubes (CNTs) films on the chemical and electronic properties of the material is reported. The CNTs were grown by the chemical vapor deposition technique (CVD) on silicon TiN coated substrates previously decorated with Ni particles. The Ni decoration and TiN coating were successively deposited by ion-beam assisted deposition (IBAD) and afterwards the nanotubes were grown. The whole deposition procedure was performed in situ as well as the study of the effect of ion-beam irradiation on the CNTs by x-ray photoelectron spectroscopy (XPS). Raman scattering, field-effect emission gun scanning electron microscopy (FEG-SEM), and field emission (FE) measurements were performed ex situ. The experimental data show that: (a) the presence of either H2+ or N2+ ions in the irradiation beam determines the oxygen concentration remaining in the samples as well as the studied structural characteristics; (b) due to the experimental conditions used i...

N-TiO: Chemical Synthesis and Photocatalysis

The chemical synthesis of nitrogen-doped titanium dioxide (N-TiO2) is explored in an attempt to understand the mechanisms of doping. Urea is used as precursor in a sol gel synthesis of N-TiO2. Chemical and structural changes during thermal treatment of the precursors were followed by several techniques. The effect of doping on band gap, morphology, and microstructure was also determined. The byproducts produced during firing correspond to those obtained during urea thermal decomposition. Polynitrogenated colored compounds produced at temperatures below 400°C may act as sensitizer. Incorporation of N in the TiO2 structure is possible at higher temperatures. Degradation experiments of salicylic acid under UVA and visible light (𝜆>400 nm) in the presence of TiO2 or N-TiO2 indicate that doping decreases the activity under UVA light, while stable byproducts are produced under visible light.

Acid Drainage and Metal Bioleaching by Redox Potencial Changes in Heavy Polluted Fluvial Sediments

Sediments from polluted urban streams act as a sink of contaminants. The high content of organic matter and sulphides makes the system appropriate for binding heavy metals. However, changes in the redox potential leads to processes in which sediments acts like a low sulphidic ore in an oxidizing environment, and could generate acid drainages. Human and not human disturbances of the sediments could derive in its oxidation catalyzed by sulphur oxidizing bacteria (SOB). This process leads to acidification and metal release. In this study we analyze the acidification potential of anaerobic sediments of polluted streams near Buenos Aires with static and kinetic methods. The results remark the necessity to consider this process before any sediment management action.

Colloidal properties of sodium caseinate-stabilized nanoemulsions prepared by a combination of a high-energy homogenization and evaporative ripening methods

Nanoemulsions stabilized by sodium caseinate (NaCas) were prepared using a combination of a high-energy homogenization and evaporative ripening methods. The effects of protein concentration and sucrose addition on physical properties were analyzed by dynamic light scattering (DLS), Turbiscan analysis, confocal laser scanning microscopy (CLSM) and small angle X-ray scattering (SAXS). Droplets sizes were smaller (~100nm in diameter) than the ones obtained by other methods (200 to 2000nm in diameter). The stability behavior was also different. These emulsions were not destabilized by creaming. As droplets were so small, gravitational forces were negligible. On the contrary, when they showed destabilization the main mechanism was flocculation. Stability of nanoemulsions increased with increasing protein concentrations. Nanoemulsions with 3 or 4wt% NaCas were slightly turbid systems that remained stable for at least two months. According to SAXS and Turbiscan results, aggregates remained in the nano range showing small tendency to aggregation. In those systems, interactive forces were weak due to the small diameter of flocs.