The properties of iron metal that make it useful in remediation of chlorinated solvents may also lead to reduction of other groundwater contaminants such as nitro aromatic compounds (NACs). Nitrobenzene is reduced by iron under anaerobic conditions to aniline with nitrosobenzene as an intermediate product. Coupling products such as azobenzene and azoxybenzene were not detected. First-order reduction rates are similar for nitrobenzene and nitrosobenzene, but aniline appearance occurs more slowly (typical pseudo-first-order rate constants 3.5 × 10-2, 3.4 × 10-2, and 8.8 × 10-3 min-1, respectively, in the presence of 33 g/L acid-washed, 18−20 mesh Fluka iron turnings). The nitro reduction rate increased linearly with concentration of iron surface area, giving a specific reaction rate constant (3.9 ± 0.2 × 10-2 min-1 m-2 L). The minimal effects of solution pH or ring substitution on nitro reduction rates, and the linear correlation between nitrobenzene reduction rate constants and the square-root of mixing ra...

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Reduction of Nitro Aromatic Compounds by Zero-Valent Iron Metal

The oxidative cross-coupling of sulfonamide antimicrobials to constituents of natural organic matter was investigated. Sulfonamide antimicrobials were incubated with surrogate humic constituents in the absence and presence of phenoloxidases (viz., peroxidase, laccase, and tyrosinase) or acid birnessite. Substituted phenols were chosen as simple model constituents to determine the structures in humic substances important for cross-coupling reactions. The extent of sulfonamide transformation was evaluated by the disappearance of the parent compound from solution. Incubation with phenoloxidases in the absence of substituted phenols resulted in little or no sulfonamide transformation. In contrast to this, direct oxidation of sulfonamides by acid birnessite was significant. Inclusion of o-diphenols and 2,6-dimethoxyphenols in reaction mixtures resulted in significant phenoloxidase-mediated transformation of sulfonamides and enhanced antimicrobial transformation in the presence of acid birnessite. Phenolic comp...

Cross-coupling of sulfonamide antimicrobial agents with model humic constituents.

Chlorinated phenols and anilines are transformed and detoxified in soil through oxidative coupling reactions mediated by enzymes or metal oxides. The reactions may be influenced by humic constituents, such as syringaldehyde or catechol, that originate from lignin decomposition and are also subject to oxidative coupling. In this study, the effect of humic constituents on xenobiotic transformation was evaluated in vitro based on the determination of unreacted chlorophenols and chloroanilines. In experiments with peroxidase, laccase, and birnessite (δ-MnO2), the transformation of most chlorophenols was considerably enhanced by the addition of syringaldehyde. Less enhancement was observed using 4-hydroxybenzoic acid, and the addition of catechol resulted in a reduction of most transformations. The opposite was observed in experiments with tyrosinase, in which case catechol caused considerable enhancement of chlorophenol transformation. The varying effect of catechol can be explained by different transformatio...

Effect of Humic Constituents on the Transformation of Chlorinated Phenols and Anilines in the Presence of Oxidoreductive Enzymes or Birnessite

The interactions of iodide ions with cuprite (Cu2O) surfaces were studied by combining batch experiments and surface analyses. The evolution of iodide uptake with pH was investigated. The thermodynamical calculations and surface analyses (X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy, and electrochemistry) were used to show that two different pH-dependent mechanisms are responsible for the accumulation of the iodide species on Cu2O. At pH values lower than 6.5, the precipitation of CuI occurs on the cuprite surface, while in more alkaline medium, the iodide adsorption takes place by substituting the surface hydroxyl groups of Cu2O. The sorption processes were not affected by a 1000-fold excess of chloride ions, but they were limited to the potential range corresponding to the stability domain of Cu2O (i.e., between −10 and +190 mV/ENH at pH 8); thus no accumulation was observed either on metallic copper or on CuO.

Gordon. Bird

Papers

Sorption of iodide on copper