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| - Enhanced Remote Photocatalytic Oxidation onSurface-Fluorinated TiO2
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| - The mobile nature of active oxygen species generated on the UV-illuminated TiO2 surface is now well-recognized. Surface oxidants not only migrate two-dimensionally but also desorb from the surface to beair-borne oxidants. The remote photocatalytic oxidation (PCO) of stearic acids over the surface-fluorinatedTiO2 (F-TiO2) film was carried out in the ambient air to study the effects of fluorination on the desorptionof oxidants from the surface. The F-TiO2 film was faced to a stearic acid-coated glass plate separated bya small gap (typically 30 μm), and the photocatalytic degradation of the stearic acid was monitored byFourier transform infrared measurement or gas-chromatographic CO2 production analysis. Remotephotocatalytic degradation of stearic acids was markedly faster with F-TiO2 than with the pure TiO2 film,which indicates that the generation of air-borne oxidants is enhanced over the F-TiO2 surface. The remotePCO activity was higher with a higher surface fluoride concentration, higher UV intensity, and smallergap. The remote photocatalytic activity of F-TiO2 was maximal at a relative humidity of 50% and did notshow any sign of deactivation with repeated reactions. The production of CO2 that evolved as a result ofthe remote PCO of stearic acids was enhanced when H2O2 vapor was present but was strongly inhibitedin the presence of ammonia gas that should scavenge OH radicals. Judging from various evidences, theair-borne oxidants in remote PCO are most likely OH radicals and the surface fluorination of TiO2 seemsto facilitate the desorption of OH radicals.
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