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| - Chain Photoreduction of CCl3F in TiO2 Suspensions: Enhancement Induced by O2
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| - Trichlorofluoromethane (CFC 11) was photoreduced in aqueous suspensions of TiO2 particles containingHCO2- ions and air. Dissolved O2 inhibited the reaction during an induction period that preceded the rapidformation of chloride ions. Reaction rates were higher in systems containing O2 as compared to analogousreactions that occurred in anaerobic suspensions. High photonic efficiencies of Cl- formation (≥15) wereachieved using suspensions with pH ≥ 5. As was the case for studies with air-free suspensions, reactions arebest described using a photoinitiated chain mechanism that produced CHCl2F and Cl- during the propagationsteps. The enhanced yields obtained in the presence of air are attributed to the removal by O2 of electronstrapped in the oxide, which are converted first into H2O2 and then into reducing radicals that participate inthe chain process. Enhanced yields of Freon photoreduction were also observed during illumination of air-free suspensions containing hydrogen peroxide, which were interpreted using a similar mechanism.
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