Titanium Dioxide-Coated Silica Waveguides for the Photocatalytic Oxidation of Formic Acid in Water

Photooxidation of organic compounds on the surface of titanium dioxide (TiO[sub 2]) is a potential method of removing organic pollutants from water. By coating TiO[sub 2] on transparent substrates and illuminating the catalyst with internally reflected light, it may be possible to increase the amount of illuminated photocatalyst in a given reactor volume. Planar, silica internal reflection elements (IREs) were coated with thin, porous, nanoparticulate films of TiO[sub 2]. UV-visible internal reflection spectroscopy was performed in order to determine that visible and near-UV light propagated through the modified IREs in an attenuated total reflection (ATR) mode. The TiO[sub 2]-coated IREs were employed in a photocatalytic reactor, and their ability to oxidize formic acid was assessed. Apparent quantum yields and quantum efficiencies of formic acid oxidation as a function of catalyst film thickness and incident angles of internally propagation UV light (310--380 nm) were determined. Quantum efficiency was enhanced when UV light propagated through the TiO[sub 2]-coated waveguide in an ATR mode. Photocatalytic reactors based on waveguide-supported TiO[sub 2] films operating in an ATR mode may utilize light more effectively than reactors based on direct irradiance of TiO[sub 2] and could facilitate the scale-up of photocatalytic oxidation processes for commercial remediationmore » applications.« less