Photoreduction processes involving

Recent work involving the binding of HOCs to DOM has also centered on how the binding phenomenon may enhance the degradation of the contaminant. A number of studies have suggested that this can occur in sunlight through photoreduction processes (Burns et al., 1996, 1997 Friesen et al.,... 

In a DISP 2 mechanism the second-order disproportionation step is rate limiting (see Section 2). An example of such a process involves the photoreduction of the dye fluorescein in basic aqueous solutions at mercury electrodes (Compton etal., 1988b). The photoreduction of benzophenone (86) and fluorobenzophenone in acetonitrile also proceeds via a DISP 2 type mechanism as verified by channel electrode voltammetry (Leslie et al., 1997). The rate-limiting step is electron transfer (86c) between photoexcited radical anion and the initial anionic species formed on electron transfer at the electrode surface. This process is further complicated by significant con-proportionation (86e) and quenching of the benzophenone excited state (86f). 

For the solid-state reduction techniques, crystals are grown containing trivalent ions, as in the photoreduction process, but the divalents produced are now stabilized. One of these techniques involves heating the trivalent crystal with the appropriate alkaline earth metal. A convenient way of doing this is to heat the crystal with the alkaline earth metal in a vacuum so that the crystal is baked in metal vapor (11). The reduction can also be carried out by solid-state electrolysis 4,7). An electric field is applied to the crystal at an elevated temperature such as above 600°C. for calcium fluoride or above 400°C. for strontium chloride. If the reduction is carried out below these temperatures, nonuniform results are obtained. 

Owing to the great interest in photoreduction reactions, electron transfer processes involving [Co (cage)] + and polypyridine-ruthenium(II) complexes have been extensively investigated. The rate constants for the quenching process range from 2 X 10 to 1 X 10 s at 25 °C. The yields of electron transfer products... 

By analogy with a reversible CO2 assimilation reaction known to occur in certain bacteria, Lipmann and Tuttle have proposed a theory explaining how carbon chains may be progressively lengthened by a process involving phosphorylation, CO2 assimilation and photoreduction. 

Compared with photooxygenation, i.e. the photochemical activation of oxygen, the definition of photoreduction is more difficult. Many photochemical processes involve redox reactions where one part of the substrate (in intramolecular reactions) or a second molecule (in intermolecular reactions) is reduced and the original substrate is oxidized (or... 

The mechanism that underlies the cross-linking of dichromated coatings remained a mystery for a very long time until Biltz and Eggert established that the process involves the photoreduction of Cr(VI) to Cr(III) ... 

Photocatalytic oxidation processes involving the use of semiconductors have gained increased attention for innovative treatment of hazardous wastes as well as photoreduction of toxic compounds and purification and disinfection of drinking water. 

This work attempts a systematic exploration of the role of FNR in thylakoid membranes. Flash induced absorbance transients linked to the electron transfer processes involving FNR have been identified in thylakoid membranes between 300 and 590 nm and its kinetics studied in the time range from about 20 us to a few sec at various experimental conditions. In this paper our attention is focussed on the mechanism of photoreduction of FNR by PSl. The absorbance transient spectra of FNR , the neutral singly reduced form, was identified between 430 and 550 nm and the kinetics of the absorbance changes were studied in membrane preparations of different FNR and Fd content. Our results show that photoreduction of FNR to FNR by PSl does not require the presence of soluble or membrane-bound Fd. 

FIG. 11 General mechanism for the heterogeneous photoreduction of a species Q located in the organic phase by the water-soluble sensitizer S. The electron-transfer step is in competition with the decay of the excited state, while a second competition involved the separation of the geminate ion-pair and back electron transfer. The latter process can be further affected by the presence of a redox couple able to regenerate the initial ground of the dye. This process is commonly referred to as supersensitization. (Reprinted with permission from Ref. 166. Copyright 1999 American Chemical Society.)... 

Because C02 is a practically inert molecule, artificial photosynthesis of C02 involves the use of large amounts of energy so it must use a clean source of energy (such as solar radiation).Therefore, the use of catalytic agent to facilitate the process allowing even take place at ambient temperature and pressure is necessary. In this case, it is also called as photocatalysis or photoreduction. 

Examples of photocurrent multiplication [1] include the photo-oxidation of formic acid and of secondary alcohols at /i-type semiconductors, and the photoreduction of oxygen at p-type semiconductors. The mechanisms involve majority carrier injection by a photogenerated intermediate, and IMPS has been used to determine the rate constant for these processes. 

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