Thermal Degradation of Tetrabromobisphenol A: Emission of Polybrominated Dibenzo-P-Dioxins and Dibenzofurans and other Organic Compounds

Paper submitted to the 31st International Symposium on Halogenated Persistent Organic Compounds (Dioxin 2011), Brussels, Belgium, 21-25 August 2011.

Structural Determination of Organic Compounds Units

Units and slides for the Structural Determination of Organic Compounds subject

Atmospheric PM and volatile organic compounds released from Mediterranean shrubland wildfires

Wildfires produce a significant release of gases and particles affecting climate and air quality. In the Mediterranean region, shrublands significantly contribute to burned areas and may show specific emission profiles. Our objective was to depict and quantify the primary-derived aerosols and precursors of secondary particulate species released during shrubland experimental fires, in which fire-line intensity values were equivalent to those of moderate shrubland wildfires, by using a number of different methodologies for the characterization of organic and inorganic compounds in both gas-phase and particulate-phase. Emissions of PM mass, particle number concentrations and organic and inorganic PMx components during flaming and smouldering phases were characterized in a field shrubland fire experiment. Our results revealed a clear prevalence of K+ and SO42- as inorganic ions released during the flaming-smouldering processes, accounting for 68 to 80% of the inorganic soluble fraction. During the residual-smouldering phases, in addition to K+ and SO42-, Ca2+ was found in significant amounts probably due the predominance of re-suspension processes (ashes and soil dust) over other emission sources during this stage. Concerning organic markers, the chromatograms were dominated by phenols, n-alkanals and n-alkanones, as well as by alcohol biomarkers in all the PMx fractions investigated. Levoglucosan was the most abundant degradation compound with maximum emission factors between 182 and 261 mg kg-1 in PM2.5 and PM10 respectively. However, levoglucosan was also observed in significant amounts in the gas-phase. The most representative organic volatile constituents in the smoke samples were alcohols, carbonyls, acids, monocyclic and bicyclic arenes, isoprenoids and alkanes compounds. The emission factors obtained in this study may contribute to the validation and improvement of national and international emission inventories of this intricate and diffuse emission source.

Organotitanias: a versatile approach for band gap reduction in titania based materials

The reduction of the band gap of titania is critically important to fully utilize its photocatalytic properties. Two main strategies, i.e. doping and partial reduction of Ti(IV), are the main alternatives available to date. Herein, we report a new synthesis strategy based on one-pot co-condensation of in situ prepared polymetallic titanium-alkoxide complexes with titanium tetrabutoxide. Using this direct reaction, it is possible to introduce organic compounds in the anatase phase, causing site distortions in the crystalline structure of the network. By using this strategy, a yellow and a black titania have been produced, with the latter showing a remarkable photocatalytic activity under visible-light.

Novel Ti/Ta2O5-SnO2 electrodes for water electrolysis and electrocatalytic oxidation of organics

Mixed metal oxide (MMO) electrodes have been applied to different technologies including chlorine production, organic compounds oxidation, water electrolysis, electroplating, etc. due to their catalytic, optical and electronic properties. Most of the existing MMO electrodes contain either toxic metals or precious metals of the platinum group. The aim of this study was to develop environmentally friendly and cost-effective MMO electrodes for water and organic compounds oxidation. Ti/Ta2O5-SnO2 electrodes of different nominal composition were prepared, and electrochemically and physically characterized. For water oxidation, Ti/SnO2 electrode with 5 at.% of Ta produced the highest electroactivity. Ti/SnO2 electrode with 7.5 at.% of Ta showed the best performance for the oxidation of methylene blue (MB). The electrocatalytic activity of the Ti/Ta2O5-SnO2 electrodes increased with the number of active layers. The maximum current of water oxidation reached 3.5 mA at 2.5 V when the electrode was covered with ten layers of Ta2O5. In case of the oxidation of 0.1 mM MB, eight and ten active layers of Ta2O5 significantly increased the electrode activity. The prepared electrodes have been found applicable for both water electrolysis and organic compounds oxidation.

Spherical activated carbon as an enhanced support for TiO2/AC photocatalysts

Titanium dioxide nanoparticles prepared in situ by sol–gel method were supported on a spherical activated carbon to prepare TiO2/AC hybrid photocatalysts for the oxidation of gaseous organic compounds. Additionally, a granular activated carbon was studied for comparison purposes. In both types of TiO2/AC composites the effect of different variables (i.e., the thermal treatment conditions used during the preparation of these materials) and the UV-light wavelength used during photocatalytic oxidation were analyzed. The prepared materials were deeply characterized (by gas adsorption, TGA, XRD, SEM and photocatalytic propene oxidation). The obtained results show that the carbon support has an important effect on the properties of the deposited TiO2 and, therefore, on the photocatalytic activity of the resulting TiO2/AC composites. Thus, the hybrid materials prepared over the spherical activated carbon show better results than those prepared over the granular one; a good TiO2 coverage with a high crystallinity of the deposited titanium dioxide, which just needs an air oxidation treatment at low-moderate temperature (350–375 °C) to present high photoactivity, without the need of additional inert atmosphere treatments. Additionally, these materials are more active at 365 nm than at 257.7 nm UV radiation, opening the possibility of using solar light for this application.