Dry Phase Titanium Dioxide-Mediated Photocatalysis: Basis for In Situ Surface Destruction of Hazardous Chemicals

Abstract

The photocatalytic oxidation of 2,4,6-trichlorophenol (TCP) on the surface of titanium dioxide (TiO₂) at varying water contents was investigated to provide fundamental data for incorporating photocatalysts into the surface of pavements to promote the destruction of spilled organic chemicals. 2,4,6-Trichlorophenol, spiked onto a thin layer of TiO₂, was degraded to 20% of its original concentration over 24 h; the release of chloride confirmed the degradation of the parent compound on the surface of the dry TiO₂. Addition of water (≥25% by weight) to the TiO₂ increased the rate of photocatalysis resulting in degradation of TCP to below detectable levels after 20 h. Based on competition studies using the hydroxyl radical scavengers, bicarbonate and 1-octanol, the proposed mechanisms for the dry phase photocatalytic degradation of TCP was oxidation by the valence band hole on the surface of the TiO₂ particle or dehalogenation by superoxide radical anions. Competition studies also confirmed that the more rapid TCP oxidation on wet TiO₂ was primarily the result of generation of hydroxyl radicals through oxidation of water by the valence band hole. The results show that dry phase TiO₂-mediated photocatalysis may be a potential system for the in situ surface destruction of chemicals that can be oxidized by nonhydroxyl radical mechanisms, such as valence band electron holes and dehalogenation processes.