In this work, the redox activity of fine diesel/biodiesel particulate matter (PM2.5) was studied in order to approach its toxicity from reactive oxygen species, due to adverse effects it may cause to human health. The oxidative potential was measured by the dithiothreitol (DTT) assay in order to study the relative contribution of water-soluble transition metals, polycyclic aromatic compounds (PAH), nitro-PAH, and quinones. It was analyzed a total of 24 samples collected from primarily diesel/biodiesel-exhausted particles from buses. The rate concentrations of PM2.5 redox activity ranged 0.020-0.069 nmol min-1 μg-1, with median at 0.040 nmol min-1 μg-1 (on average, 0.042 ± 0.005 nmol min-1 μg-1 for morning, 0.033 ± 0.007 nmol min-1 μg-1 for afternoon and 0.045 ± 0.009 nmol min-1 μg-1 for night). The transition metals appear to dominate the DTT response, since they were responsible up to 89% of redox activity measured in the samples. Apparently, the metal fraction contained in PM2.5 demonstrated a greater ability to catalyze reactions that promote the formation of reactive oxygen species when compared to organic compounds. It was observed that the oxidative potential of PM2.5 particles emitted from diesel/biodiesel (B7) is similar to diesel-emitted particles.

In this study, it is reported the fractal dimension and morphology of ultrafine particles emitted by a diesel engine run with B4, B50, and B100. Transmission electron micrographs evidenced two main groups of particles with characteristic and distinct morphological behaviors: (i) particle agglomerate structures self-organized within a fractal-like geometry, and (ii) amorphous and irregular particles with diffuse edges in a liquid-like particle appearance, mainly associated with some sub-fractions of samples collected from B50 and B100 combustion. Particles from (i) showed typical diesel soot morphology and fractal dimension. Primary particle diameter (Dpp) was 24 ± 4 nm, 23 ± 4 nm, and 20 ± 4 nm for B4, B50, and B100, respectively. Mean aggregate gyration diameters (Dg) ranged from 242 ± 140 nm for B4, 210 ± 135 nm for B50, and to 232 ± 140 nm for B100. In turn, fractal dimensions (Df) were 1.94, 1.89, and 1.99 for B4, B50, and B100, respectively. On the other hand, particle from (ii) had their morphology impaired from the addition of biodiesel to petrodiesel in a way it did not follow a fractal geometry.

Nb-substituted goethites have been prepared and characterized by Mössbauer spectroscopy, XRD, SEM and BET surface area measurements. Mössbauer and XRD analyses suggested that Nb replaces Fe3+ in the structure with duplet formation. The insertion of Nb into the goethite structure caused a significant increase in the BET surface area of the material. The prepared alpha-Fe1-xNb xOOH was investigated for the H2O2 decomposition to O2 and for the Fenton reaction to oxidize the dye methylene blue. It was observed that the introduction of Nb in to goethite produced a strong increase in the activity of oxidation of the dye contaminant by H2O2.