Christian Gonçalves Alonso

Drug release profile and reduction in the in vitro burst release from pectin/HEMA hydrogel nanocomposites crosslinked with titania

This work describes the drug release profile and the initial burst release from covalent hydrogel nanocomposites composed of pectin, hydroxyethyl methacrylate (HEMA) and titania (TiO2). Vitamin B12 (Vit-B12), a highly water-soluble substance, was used as a model drug. We studied the water transport profiles over a wide pH range, the moduli of elasticity (E), the morphological properties and the Vit-B12 release kinetics from these hydrogels. The initial release burst was reduced by crosslinking titania with vinylated pectin and HEMA. A reduction of up to ca. 60% was observed when compared with pure pectin/HEMA hydrogel. To gain insight into the burst release phenomenon, the experimental data were adjusted to diffusive-based models that include a rate constant of release (k). A decrease in the values of k was related to a reduction in the burst effect. The release mechanism of Vit-B12 from the pure hydrogels was governed by both Fickian diffusion and macromolecular relaxation, which are the driving forces for release. Upon addition of titania, the contribution of macromolecular relaxation to the release was minimized, suggesting a tendency towards Fickian diffusion. Furthermore, titania played a significant role in improving mechanical properties. Hydrogel nanocomposites showed a marked increase in E compared with pure hydrogels. This increase was found to be the result of an apparent increment in the cross-linking density, owing to chemical bonds of titania with the hydrogel. The proposed materials were demonstrated to be biocompatible with cells, showing good pharmacological potential.

Temperature Effect on Hydrogen Production from Reactions between Ethanol and Steam in the Presence of Pd-Ru/Nb2O5-TiO2 Catalyst

Temperature effect on the performance of Pd-Ru/Nb2O5-TiO2 (PRNT) catalyst on hydrogen production from reactions between ethanol and steam was evaluated. Parallel reactions occurred in all conditions studied according to what was observed by the presence of H2, CO2, CH4, CO, C2H4, C2H6, C2H4O and (C2H5)2O. While at 300 °C the process seems to be dominated by ethanol dehydrogenation and decomposition, at 375 °C dehydration it seems to compete for active sites with ethanol dehydrogenation and decomposition reactions. At 450 °C there is a dehydration reaction to ethane, basically competing at the same level with ethanol dehydrogenation decomposition reactions. Hydrogen production on PRNT catalyst is maximized at 300 °C.

Effect of phase composition on the photocatalytic activity of titanium dioxide obtained from supercritical antisolvent

Photocatalytic activity of TiO2 nanoparticles is highly dependent on their phase composition. The coexistence of anatase and rutile phases in a single nanoparticle eases the electron transfer process between the phases, and favors the separation of photogenerated pairs. In this work, highly photoactive mixed-phase TiO2 nanostructures were prepared by supercritical antisolvent precipitation (SAS), an environmentally friendly technology. It is shown here that this methodology has the remarkable ability to produce highly porous (515 m2/g) and crystalline TiO2 nanoparticles. The phase composition of as-prepared TiO2 samples can be tailored through annealing process. Several mixed-phase TiO2 samples were tested to assess the correlation between photocatalytic activity and phase composition. The photocatalytic performance is strongly affected by the anatase-rutile ratio, since the synergism between phases enhances the charge separation, reducing the recombination effect of the photogenerated pairs (e-/h+). It was found that the nanocatalyst composed by 7.0 wt% of rutile phase and 93.0 wt% of anatase phase, named as TiO2_650, presented the highest photodegradation for both methyl orange (MO) and methylene blue (MB) dyes. Interestingly, TiO2 samples prepared by SAS have superior photoactivity than the benchmark photocatalyst names as P25, which is a widely used TiO2 material composed of anatase and rutile phases.