Photoenhanced Uptake of NO₂ by Pyrene Solid Films

We report uptake kinetics measurements of the heterogeneous reaction of gas phase NO2 with solid films of pyrene. By using a coated flow tube equipped with several near-ultraviolet (UV) emitting lamps (range 300−420 nm), we examined the effect of actinic radiation on the heterogeneous loss kinetics of nitrogen dioxide. With atmospherically relevant concentrations of NO2, (20−119 ppbv), the uptake ranged from below 10−7 in the dark to 3.5 × 10−6 under near-UV irradiation. Under illuminated conditions, the uptake coefficient decreased markedly with increasing gas-phase concentration, suggestive of a Langmuir−Hinshelwood-type surface reaction mechanism. The NO2 reactivity was not a function of deposited Pyrene mass or of the relative humidity (in the range 10−89%) and depended linearly on the intensity of illumination. Gas-phase product analysis indicated that approximately 50% of the NO2 loss could be accounted for by HONO and NO release. These experimental results are discussed along with a possible nitration mechanism

Reactive Uptake of Ozone by Chlorophyll at Aqueous Surfaces

We report the results of two complementary studies of the heterogeneous reaction between gas-phase ozone and aqueous chlorophyll. In the first experiment, the chlorophyll is present at the air–water interface and its concentration is measured as a function of time, using laser-induced fluorescence, to obtain the surface kinetics. Under most experimental conditions, these are well described using a Langmuir–Hinshelwood formalism. The second experiment was carried out in a wetted-wall flowtube apparatus and measured the uptake coefficient of ozone by the chlorophyll solution. The uptake coefficient decreases with increasing ozone concentration, consistent with the surface mechanism found in the fluorescence experiment. The two experiments agree that the uptake coefficient for ozone by such chlorophyll samples is ∼2–5 × 10−6 with unpolluted boundary layer ozone concentrations. At low wind speed, the reaction between ozone and chlorophyll at the sea surface may represent the driving force for ozone deposition at the ocean surface, significantly increasing its deposition velocity there

Assessment of the Fe(III)–EDDS Complex in Fenton-Like Processes: From the Radical Formation to the Degradation of Bisphenol A

The present work describes, for the first time, the use of a new and strong complexing agent, ethylenediamine-<i>N</i>,<i>N</i>′-disuccinic acid (EDDS) in the homogeneous Fenton process. The effect of H₂O₂ concentration, Fe­(III)–EDDS concentration, pH value, and oxygen concentration on the homogeneous Fenton degradation of bisphenol A (BPA) used as a model pollutant, was investigated. Surprisingly, the performance of BPA oxidation in an EDDS-driven Fenton reaction was found to be much higher at near neutral or basic pH than at acidic pH. Inhibition and probe studies were conducted to ascertain the role of several radicals (e.g., ^•OH, HO₂^•/O₂^•–) on BPA degradation. This unexpected effect of pH on Fenton reaction efficiency could be due to the formation of HO₂^• or O₂^•– radicals and to the presence of different forms of the complex Fe­(III)–EDDS as a function of pH. Indeed, the reduction of Fe­(III)–EDDS to Fe­(II)–EDDS is a crucial step that governs the formation of hydroxyl radical, mainly responsible for BPA degradation. In addition to its ability to maintain iron in soluble form, EDDS acts as a superoxide radical-promoting agent, enhancing the generation of Fe­(II) (the rate limiting step) and therefore the production of ^•OH radicals. These results are very promising because they offer an important new treatment option at higher range of pH values and more particularly at pHs encountered in natural conditions

Toward a Better Understanding of Fe(III)–EDDS Photochemistry: Theoretical Stability Calculation and Experimental Investigation of 4-<i>tert</i>-Butylphenol Degradation

The present work describes in detail the chemical structure of the complex Fe­(III)–EDDS and the predominance of different species with respect to pH. These results were obtained with ab initio calculations. From the photoredox process, the formation of hydroxyl radical was confirmed, and HO^• is the main species responsible for the degradation of the organic compound present in aqueous solution. The degradation of 4-<i>tert</i>-butylphenol (4-<i>t</i>-BP), used as a model pollutant, was investigated in different conditions. For the first time, the second-order rate constant of the reaction between HO^• and 4-<i>t</i>-BP and the formation rate of HO^• (<i>R</i>_HO•^f) from the photochemical process were evaluated. Through the degradation of 4-<i>t</i>-BP, the effect of Fe­(III)–EDDS concentration, oxygen, and pH was also investigated. The pH, which plays a role in the iron cycle and in the Fe­(III)–EDDS speciation, was noticed as an important parameter for the efficiency of 4-<i>t</i>-BP degradation. Such a result could be explained by taking into account the complex speciation and presence of a predominant form (FeL^–) up to pH 8. These results are very useful for the use and optimization of such iron complexes in water treatment processes