Titanium dioxide-coated silica waveguides for the photocatalytic oxidationof formic acid in water

Photooxidation of organic compounds on the surface of titanium dioxide (TiO 2) is a potential method of removing organic pollutants from water. By coat ing TiO2 on transparent substrates and illuminating the catalyst with inter nally reflected light, it may be possible to increase the amount of illumin ated photocatalyst in a given reactor volume. Planar, silica internal refle ction 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 modifie d IREs in an attenuated total reflection (ATR) mode. The TiO2-coated IREs w ere employed in a photocatalytic reactor, and their ability to oxidize form ic acid was assessed. Apparent quantum yields and quantum efficiencies of f ormic acid oxidation as a function of catalyst film thickness and incident angles of internally propagating UV light (310-380 nm) were determined. Qua ntum efficiency was enhanced when UV light propagated through the TiO2-coat ed waveguide in an ATR mode. Photocatalytic reactors based on waveguide-sup ported TiO2 films operating in an ATR mode may utilize light more effective ly than reactors based on direct irradiance of TiO2 and could facilitate th e scale-up of photocatalytic oxidation processes for commercial remediation applications.