C. Giannotti

Solar photodegradation of pesticides in water by sodium decatungstate

Solar photodegradation in aqueous solutions of phenol, 4-chlorophenol, 2,4-dichlorophenol, bromoxynil, atrazine, imidachloprid and oxamyl, in the presence of two photocatalysts titanium dioxide TiO2 and sodium decatungstate Na4W10O32 is reported. TiO2 appears to be the most efficient photocatalyst concerning the rate of photodegradation and mineralization of the pure compounds. However, when the pesticides are used in formulated solutions, the decatungstate anion becomes as efficient or even more efficient than TiO2. The mechanism of the photodegradation in the presence of Na4W10O32 is investigated by nanosecond flash-photolysis experiments, and is compared to the one proposed for TiO2. The difference of reactivity between the two photocatalysts is accounted by the different primary processes of the mechanisms. The formulation effect is investigated with two model surfactants SDS and Triton X100, and 2-chlorophenol as a model pesticide.

Insertions photochimique et spontanée d'oxygène dans les liaisons cobaltcarbone des alcoylcobaloximes

Abstract Some alkyl(pyridinato)cobaloximes irradiated with visible light insert molecular oxygen into the cobaltcarbon bond to give stable peroxidic compounds; the alkyldioxycobaloximes. This insertion reaction also occurs without light with alkylcobaloximes having a cobaltcarbon bond in a benzylic position.

Photolysis of dialkyl metallocenes of the titanium group; an ESR study

Abstract Photolysis in the visible and the UV region of dialkyl metallocenes of the titanium group is studied by ESR. The primary process is shown to be homolytic cleavage of the metal—alkyl bond, with formation of paramagnetic metal species and organic free radicals. The first were identified from the ESR signal produced and the second from the spectra of their spin adducts with the appropriate spin trap. The M C bond cleavage depends on the metal and on the radiation wavelength.

Interaction of porphyrin and metalloporphyrin excited states with molecular oxygen. Energy-transfer versus electron-transfer quenching mechanisms in photo oxidations

Abstract An investigation of the quenching of porphyrin and metalloporphyrin excited states by oxygen in protic and aprotic organic solvents is reported. Studies using spin traps in the ESR together with an investigation of photooxidation behavior indicate that both superoxide ion and singlet oxygen are formed in the quenching process for several porphyrins. For the palladium complex, PdOEP, it has been determined that irreversible branching occurs in the quenching prior to the formation of free superoxide.

Study of the mechanisms of the photodegradation of atrazine in the presence of two photocatalysts: TiO2 and Na4W10O32

The mechanisms of the photodegradation of atrazine under direct photolysis and in the presence of two different photocatalysts, TiO2 and Na4W10O32, are investigated by the means of GC/MS, total radioactivity counting, HPLC and TLC analysis on 14C ring-labelled atrazine solutions. Integration of photo- and biodegradation processes is studied.

Etude de quelques facteurs influencant l'insertion photoinduite d'oxygene dans la liaison cobalt—carbone des alcoylcobaloximes

Abstract The photo-induced insertion of oxygen into the cobalt—carbon bond of alcoylcobaloximes occurs by the way of a pentacoordinated complex obtained by photolytic cleavage of the cobalt—base bond. This bond is reformed immediately after the insertion of oxygen to give the alkylperoxycobaloxime.

Photo-oxidation of alkanes by metal oxide semiconductors

Abstract The partial conversion of alkanes to the corresponding ketones has been achieved by irradiation of a suspension of semiconductor powder in oxygen-saturated alkanes. The reactivity of thermally and chemicallydoped semiconductor and the effect of chemisorbed water have also been studied.

Photochemical substitution reactions of some alkylcobaloximes by hydroperoxides and the crystal structure of cumyl peroxide (pyridine) cobaloxime

Abstract Alkyl(pyridine) cobaloximes irradiated with visible light in the presence of tert-butyl or cumyl hydroperoxide give rise to tert-butyl or cumyl peroxide(pyridine)cobaloxime by photochemical substitution reaction. We report the structure of the cumyl peroxide(pyridine)cobaloxime determined by X-ray diffraction

Photocatalytic degradation of 5-nitro-1,2,4-triazol-3-one NTO in aqueous suspention of TiO2. Comparison with Fenton oxidation.

5-nitro-1,2,4-triazol-3-one (NTO) is a powerful insensitive explosive, present in industrial waste waters. A remediation method based on photochemical decomposition and Fenton oxidation of NTO has been evaluated by monitoring the mineralization of 14C-labelled NTO. The TiO2-catalyzed photodegradation (lambda > 290 nm, TiO2 0.4 g/l, NTO 150 mg/l)) leads to the complete mineralization of NTO in 3 hours. This degradation involves a simultaneous denitrification and ring scission of NTO leading to nitrites, nitrates and carbon dioxide. No significant photo-degradation of NTO was detected in the absence of the catalyst. Long term irradiation over one week, leads to a complete degradation of concentrated NTO (5 g/l), suggesting that this method could be useful to clean-up NTO wastes. Fenton oxidation offers an efficient cost-effective method for NTO remediation. This reaction is faster that the TiO2 catalyzed photolysis and find application on the mineralization of high concentrations of NTO (15 g/l). Fenton oxidation provokes ring cleavage and subsequent elimination of the two carbon atoms of NTO as CO2. During this reaction, the nitro group is completely transformed into nitrates.

Electron spin resonance studies of the anaerobic and aerobic photolysis of alkylcobaloximes

Abstract Aerobic and anaerobic photolysis of methyl(pyridine)cobaloxime, benzyl(pyridine)cobaloxime and analogous compounds in CHCl3 results only in an electron transfer reaction from an equatorial ligand producing photo-reduction of CoIII to CoII, the complex retaining its axial ligands. If after the anaerobic photolysis of benzyl(pyridine)cobaloxime the oxygen is introduced without any further photolysis we obtain an ESR spectrum of nitroxide, arising from the attack of a benzyl radical on the dimethylglyoxime equatorial ligand. For the other complexes, homolytic cleavage of the CoC bond occurs and in the presence of oxygen gives rise to the superoxide cobalt complex adduct Py(CoIIIO2−. During photolysis of methyl(pyridine)cobaloxime in isopropanol homolytic cleavage of the CoC bond occurs in preference to electron transfer reaction from the equatorial ligands. The anaerobic photolysis of benzyl(pyridine)cobaloxime in isopropanol or in water at 113–133 K results in an electron transfer reaction. However, at 170 K we observe the formation of the CoII complex arising from CoC bond cleavage. A mechanism for photo-induced insertion of oxygen in the CoC bond is proposed.