Photocatalytic Dechlorination of Air Free Aqueous Carbon Tetrachloride Solutions in TiO2 Layer Systems. A Chain Reaction Mechanism

Johannes Stark, Joseph Rabani

Research output: Contribution to journalArticlepeer-review

Abstract

Quantum yields of chloride ions exceeding unity are observed upon illumination of TiO2 layers in aqueous solutions containing CCl4 and methanol. The layers were produced by spin coating of TiO2 (prepared by hydrolysis of the propoxide) from concentrated colloid solutions. Absorbed light intensities ranged from 7×10-11 to 3×10-8 ein cm-2s 1. No effect of alcohol concentration on the yield is observed in the range 0.01-12 M. A negligible yield of chloride ion is obtained in the absence of methanol. Pre-equilibration of the layer with the CCl4 solution proved necessary for maximization of the yields of photo-dechlorination. The rate of build up of the chloride ions increases nearly linearly with the square root of the light intensity at the lowest intensities which were employed. At the lowest intensity, the quantum yield ϕ (corrected for dark reaction) increases from ≍1 in the ϕ range 2-6 to ϕ > 6 at PH 12.2. There is no observable effect of CCl4 concentration above 1 mM. The high quantum yields and the roughly square root dependence on light intensity (at very low intensities) indicate that a chain reaction takes place.

Original languageEnglish
Pages (from-to)93-98
Number of pages6
JournalZeitschrift fur Physikalische Chemie
Volume213
DOIs
StatePublished - Jan 1999

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