Photocatalytic oxidation of organic compounds via waveguide-supported titanium dioxide films

A photochemical reactor based on titanium dioxide (TiO₂)-coated silica optical fibers was constructed to explore the use of waveguide-supported TiO₂ films for photocatalytic oxidation of organic compounds. The reactor was used for the photocatalytic oxidation of 4-chlorophenol in water. It was confirmed that TiO₂ films could be securely attached to silica optical fibers. The 4-chlorophenol (100 μmol/L in water) was successfully oxidized on the TiO₂ surface when UV light (310 nm–380 nm) was propagated through the fibers to the films. Rates of 4-chlorophenol oxidation and UV light flux to the fibers were measured.; The quantum efficiency of 4-chlorophenol oxidation [defined as the change in 4-chlorophenol concentration divided by the UV light absorbed by the catalyst] was determined as a function of TiO₂ catalyst film thickness and internal incident angle of propagating UV light. A maximum quantum efficiency of 2.8% was measured when TiO₂ film thickness was ca. 80 nm and the maximum internal incident angle of propagating light was 84°. Quantum efficiency increased with increasing internal angle of incidence of propagating light and decreased with TiO₂ film thickness.; UV-Visible internal reflection spectroscopy was used to determine whether UV light propagated through TiO₂-coated silica waveguides in an ATR mode. Propagation of UV light in an ATR mode was confirmed by the similarities between internal reflection spectra of phenolphthalein obtained with uncoated and TiO₂-coated silica crystals.; Planar silica waveguides coated with TiO₂ were employed in a photocatalytic reactor for the oxidation of formic acid (833 μmol/L in water). It was shown that the quantum yield of formic acid oxidation [defined as the moles of formic acid oxidized divided by the moles of UV photons absorbed by the catalyst] on the waveguide-supported TiO₂ surface is enhanced when UV light propagates through the waveguides in an ATR mode. A maximum quantum yield of 3.9% was found for formic acid oxidation on silica waveguides. The waveguides were coated with 150 nm of TiO₂ and activated with UV light (λ_max = 360 nm) propagating through the waveguides at an internal incident angle of 68°.