| The photocatalytic oxidation of thin ({dollar}approx{dollar}1 mm) organic films on water by TiO{dollar}sb2{dollar} coated buoyant microspheres was investigated using near UV light (3-5 mW/cm{dollar}sp2{dollar}, 365 nm max. irradiance). The rates of O{dollar}sb2{dollar} and hydrocarbon consumption, the rate of CO{dollar}sb2{dollar} production, and the selectivity of the oxidation reactions were studied for model hydrocarbons (octane, 3-octanol, 3-octanone, octyl aldehyde, octanoic acid, and benzene). Experimental results involving dissolved Fe{dollar}sp{lcub}3+{rcub}{dollar} ions and oxygen incorporation into the model hydrocarbons suggest that not only the photogenerated holes, but also photogenerated electrons participate in the oxidation reactions. Dioxygen has two roles: it accepts the electron generated in the TiO{dollar}sb2{dollar} crystallite and is reduced to a superoxide radical (O{dollar}sb2sbsp{lcub}cdot{rcub}{lcub}{lcub}-{rcub}{rcub}{dollar} or {dollar}cdot{dollar}OOH), and reacts with the hole-generated carbon radical forming an organoperoxyl radical (ROO{dollar}cdot{dollar}). The superoxide radical combines with the organoperoxyl radical forming an unstable tetraoxide that decomposes.; During TiO{dollar}sb2{dollar} photocatalysis, the decomposition reaction pathways involve the formation of tetraoxides formed during the termination reaction between two peroxy radicals (organo-tetraoxides) or between a peroxyl radical and hydroperoxyl radical (organo-hydrotetraoxides). Proposed reaction mechanisms account for the observed dioxygen consumption rates during electron depolarization reactions (e{dollar}sp{lcub}{lcub}-{rcub}{rcub}{dollar} + O{dollar}sb2 to{dollar} O{dollar}sb2sbsp{lcub}cdot{rcub}{lcub}{lcub}-{rcub}{rcub}{dollar}; {dollar}cdot{dollar}OOH {dollar}rightleftharpoons{dollar} O{dollar}sb2sbsp{lcub}cdot{rcub}{lcub}{lcub}-{rcub}{rcub}{dollar}; + H{dollar}sp+{dollar}; ROO{dollar}cdot{dollar} + {dollar}cdot{dollar}OOH {dollar}to{dollar} products) and are consistent with observed products during the PCO of model hydrocarbons.; During the oxidation of crude oil the photocatalytic process is inefficient (the observed quantum yield is on the order of 1 to 2%). Therefore, using naturally occurring nonconcentrated solar radiation, photocatalysis may have limited potential for oil spill remediation of thin films. Even at high bead to oil ratios, the solar assisted photocatalytic oxidation of crude oil takes several months. However, the oleophilic microbubbles can absorb oil films forming aggregates (at a ratio less than about 1 ml per g photocatalytic cenosphere or 2 ml per g photocatalytic microbubble) that prevent the formation of heavier than water tar-like residue and emulsification attributed to polymerization of polyaromatic hydrocarbons. Furthermore, these oil-bead aggregates can be readily collected, burned, or by long term exposure to solar radiation, oxidized to CO{dollar}sb2{dollar}, water, and water soluble compounds. |
