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

Abstract

Photooxidation of organic compounds on the surface of titanium dioxide (TiO2) is a potential method of removing organic pollutants from water. By coating TiO2 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 TiO2. 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 TiO2-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 propagating UV light (310−380 nm) were determined. Quantum efficiency was enhanced when UV light propagated through the TiO2-coated waveguide in an ATR mode. Photocatalytic reactors based on waveguide-supported TiO2 films operating in an ATR mode may utilize light more effectively than reactors based on direct irradiance of TiO2 and could facilitate the scale-up of photocatalytic oxidation processes for commercial remediation applications.