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Persulfate (PS) activated by zero-valent iron (ZVI) to generate sulfate radicals (SO4 •–) was employed in the oxidation of Orange G (OG), an azo dye commonly found in textile wastewaters. Acidic corrosion and direct reaction with persulfate were considered for the oxidation of ZVI to Fe­(II), both reactions taking place at the ZVI surface. Effects of pH (1–3.5), PS concentration (0 and 1 mM), and ZVI particle radius (0.030–0.095 cm) were studied. OG (0.1 mM) oxidation was carried out with a 0.5 L batch reactor at 20 °C. Using ZVI as activator, Fe­(II) is slowly released to the media through a fluid–solid corrosion of ZVI. Therefore, the unproductive consumption of sulfate radicals by Fe­(II) can be controlled by changing the particle diameter. A kinetic model capable of describing the evolution of pollutant, oxidant, and iron concentrations (at the different oxidation stages) as well as the mineralization was proposed and validated. To do this, a set of reactions counting for the iron valence change, the sulfate radical production, and the pollutant oxidation and mineralization have been proposed, and the kinetic parameters have been estimated from fitting experimental data. In addition, the model was able to predict data obtained using Fe­(II) and Fe­(III) as activator. Regeneration of Fe­(III) into Fe­(II) by the organic matter was also considered as found elsewhere (Rodriguez, S.; et al. Oxidation of Orange G by persulfate activated by Fe­(II), Fe­(III) and zero valent iron (ZVI). Chemosphere 2014, 101, 86–92).

Isotopic fractionation of volatile organic compounds (VOCs), which are under strict measures of control because of their potential harm to the environment and humans, has an important ecological aspect, as the isotopic composition of compounds may depend on the conditions in which such compounds are distributed in Nature. Therefore, detailed knowledge on isotopic fractionation, not only experimental but also based on theoretical models, is crucial to follow conditions and pathways within which these contaminants are spread throughout the ecosystems. In this work, we present carbon and, for the first time, bromine vapor pressure isotope effect (VPIE) on the evaporation process from pure-phase systems-dibromomethane and bromobenzene, the representatives of aliphatic and aromatic brominated VOCs. We combine isotope effects measurements with their theoretical prediction using three computational techniques, namely path integral molecular dynamics, QM cluster, and hybrid ONIOM models. While evaporation of both compounds resulted in normal bromine VPIEs, the difference in the direction of carbon isotopic fractionation is observed for the aliphatic and aromatic compounds, where VPIEs are inverse and normal, respectively. Even though theoretical models tested here turned out to be insufficient for quantitative agreement with the experimental values, cluster electronic structure calculations, as well as two-layer ONIOM computations, provided better reproduction of experimental trends.