Phototransformation of ibuprofen and ketoprofen in aqueous solutions.

The UV (254 nm) and UV/VUV (254/185 nm) photolysis of two anti-inflammatory drugs, ibuprofen and ketoprofen, have been studied in aqueous solutions as a possible process for the removal of non-biodegradable compounds. We have examined the effects of dissolved oxygen and initial target concentration. Upon irradiation at 254 nm, the decomposition rate of ketoprofen is almost forty times higher as it of ibuprofen whilst VUV irradiation only increased the ibuprofen decomposition rate. The presence of dissolved oxygen accelerated the photodegradation of ibuprofen, whereas no effect was observed on the degradation of ketoprofen. The maximum quantum yield for the phototransformation was 0.2. The rate of mineralization in both cases was ∼60%, even after 1h of treatment and this suggests the formation of stable by-products which were identified using GC-MS and HPLC-MS, respectively.

Phototransformation of diuron in aqueous solution by UV irradiation in the absence and in the presence of H2O2.

The phototransformation of diuron has been studied by photolysis at 253.7 nm at 20 degrees C, in the absence and in the presence of H2O2. Experiments were conducted in batch and in continuous-flow reactors. In the absence of H2O2, the value of the quantum yield of photolysis of diuron at 253.7 nm was found to be equal to be 0.0125 +/- 0.0005 (using a molar absorption coefficient of 16500 +/- 500 M(-1) cm (-1) at 253.7 min) and insensitive to pH in the range 2-8.5. Oxidation rates of diuron by H2O2/UV could be predicted successfully by a kinetic model including photochemical and OH*-oxidation reactions using a value of 4.6 x 10(9) M(-1) s(-1) for the rate constant of the reaction of OH* with diuron. The model was verified for the various reactors used and under a wide range of conditions in pure water (pH: 2-8, [H2O2] : 0-0.1 M) and in the presence of hydrogenocarbonate ions (0-35 mM, pH = 8.3-8.4). The contribution of the carbonate radicals to the degradation rates of diuron was found to be insignificant under our experimental conditions.

Diuron degradation in irradiated, heterogeneous iron/oxalate systems: the rate-determining step.

The purpose of this study was to examine the various factors that control the kinetics of diuron degradation in irradiated, aerated suspensions containing goethite (alpha-FeOOH) and oxalate, in the following denoted as heterogeneous photo-Fenton systems. In these systems, attack by hydroxyl radicals (HO.) was the only pathway of diuron degradation. Studies were conducted in systems containing initially 80 or 200 mg L(-1) goethite (corresponding to 0.9 or 2.25 mM total iron) and 20, 50, 75, 100, 200, and 400 microM oxalate at 3 < or = pH < or = 6. Both oxalate concentration and pH greatly affected the rate of light-induced diuron transformation. In the presence of initial 200 microM oxalate, the rate of diuron degradation was maximal at pH 4, coinciding with the maximal extent of oxalate adsorption on the surface of goethite. At pH 4,the rate of light-induced diuron degradation increased with increasing oxalate concentration, reaching a plateau at initial 200 microM oxalate, i.e., at the oxalate solution concentration at which the extent of oxalate adsorption on the surface of goethite reached a maximum. These experimental results suggest that the rate of Fe(II)(aq) formation through photochemical reductive dissolution of goethite, with oxalate acting as electron donor, determines the kinetics of diuron degradation in these heterogeneous photo-Fenton systems.

3-Chlorophenol elimination upon excitation of dilute iron(III) solution: evidence for the only involvement of Fe(OH)2+.

The transformation of 3-chlorophenol (3CP) photoinduced by iron(II) in aqueous solution has been investigated under monochromatic irradiation (lambda(exc) = 365 nm) representative of atmospheric solar emission. Hydroxyl radicals are formed via an intramolecular photoredox process in iron(III) excited hydroxy-complexes. Fe(OH)2+ is the most active complex in terms of HO* formation and according to our experiments and calculations, it appears that Fe(OH)2+ is the only iron(III) species involved in 3CP oxidation process. Hydroxyl radicals react very rapidly with 3CP, which is eliminated from the solution. The primary intermediates do not accumulate in the medium but rapidly degraded to non-absorbing compounds by a subsequent action of hydroxyl radicals.