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.

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.

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.

Purification and functionalization of carbon nanotubes by classical and advanced oxidation processes.

Advanced oxidation technologies (AOT) were applied for the production of accurately controlled oxidized multi-walled carbon nanotubes. Fenton process is effective to get carboxylic (-COO- or -COOH) and OH groups on the surface of carbon nanotubes while Photofenton and UV/H2O2 processes mostly produce OH groups on surface of multiwalled carbon nanotubes (MWCNT). All of them preserve the structure of MWCNT allowing to achieve accurately controlled oxidized MWCNT. Fourier transform infrared spectroscopy (FTIR) and thermogravimetical analysis (TGA) show that the acid treatment is the more efficient technique to generate COOH groups on MWCNT surface. However, this chemical technique generates strong damages on the MWCNT structure, as demonstrated by TGA, field emission scanning electron microscopy and transmission electron microscopy results.

Photocatalyzed degradation of flumequine by doped TiO2 and simulated solar light.

Titanium dioxide was obtained in its pure form (TiO2) and in the presence of urea (u-TiO2) and thiourea (t-TiO2) using the sol-gel technique. The obtained powders were characterized by BET surface area analysis, Infrared Spectroscopy, Diffuse Reflectance Spectroscopy and the Rietveld refinement of XRD measurements. All the prepared catalysts show high anatase content (>99%). The a and b-cell parameters of anatase increase in the order TiO2u-TiO2>TiO2. The photocatalytic activities of the samples were determined on flumequine under solar-simulated irradiation. The most active catalysts were u-TiO2 and t-TiO2, reaching values over 90% of flumequine degradation after 15 min irradiation, compared with values of 55% for the pure TiO2 catalyst. Changing simultaneously the catalyst amount (t-TiO2) and pH, multivariate analysis using the response surface methodology was used to determine the roughly optimal conditions for flumequine degradation. The optimized conditions found were pH below 7 and a catalyst amount of 1.6 g L(-1).

Photooxidation of organic mixtures on biased TiO2 films.

Processes that occur in the TiO2-photocatalysis of binary aqueous solutions containing model photolytes with different affinity for the TiO2 surface (methanol and oxalic and salicylic acids) are analyzed from the photoelectrochemical response of TiO2 films under bias in a time window of 1-100 s. Long-lived oxidized intermediates produced upon illumination at 0.6 VSCE are detected by cathodic sweep run in the dark after irradiation. The main conclusion derived from this work is that a scheme of competitive kinetics describes only those cases in which one of the components is weakly or nonadsorbed on TiO2, whereas for two photolytes with high affinity for the surface cooperative effects may occur. The methanol-oxalate system is quantitatively modeled by considering that oxalate forms surface complexes with different reactivity and a parallel pathway for hole transfer to -OH and adsorbed oxalate. In this case as well as for electrolytes containing methanol and salicylate photooxidation of methanol (with low affinity for the surface) via intermediates formed by reaction with trapped holes (-*OH) is partially or fully suppressed. For electrolytes containing oxalic and salicylic acids in which both components chemisorb on TiO2 the photoelectrochemical response depends on preadsorption, the photooxidation pathways deviates those of single component systems, and there is remotion of salicylate adsorbed byproducts assigned to cooperative effects.