Quantitative photocatalyzed soot oxidation on titanium dioxide

We report here the titanium dioxide (TiO2) photocatalyzed oxidation of deposited hurricane lamp soot. Sol–gel derived TiO2 was coated on quartz crystal microbalance (QCM) elements. Characterization by spectroscopic ellipsometry (SE) and atomic force microscopy (AFM) revealed low surface roughness of 0–17%, and SE showed a linear variation of the TiO2 thickness versus the number of sol–gel spin coats.Soot was deposited on the calcined TiO2 film using an analytical rotor passing through a hurricane lamp flame, and subsequently irradiated with near-UV light. Varying the soot mass on the TiO2-coated QCM crystals revealed behaviors over 20,000 min ranging from total soot destruction of a single pass soot layer to minimal oxidation of an eight pass soot layer, the latter caused by soot screening of the incident UV light. A series/parallel reaction mechanism [P. Chin, G.W. Roberts, D.F. Ollis, Industrial & Engineering Chemistry Research 46 (2007) 7598] developed to describe previous literature data on TiO2-catalyzed soot photooxidation was successfully employed to capture the longer time changes in presumably graphitic soot mass as a function of UV illumination time from 1000 to 20,000 min and of soot layer thickness. Short time soot mass loss is attributed to oxidation of organic carbons deposited on the graphitic soot components. This kinetic model can be used to predict the rate of TiO2-catalyzed soot destruction as a function of near-UV illumination time and initial soot layer thickness.