We developed earlier¹ a series/parallel kinetic model for direct photocatalytic soot oxidation by thin films of TiO₂ and successfully used it to analyze the experimental CO₂ generation data of Mills et al.² and the soot mass loss data of Lee and Choi³. The model assumes two oxidation pathways: a single step yielding CO₂ directly, and a serial sequence through a solid intermediate species, which is subsequently oxidized to CO₂.

In the present work, laboratory studies of photocatalyzed soot oxidation are conducted using a quartz crystal microbalance (QCM). Hurricane lamp soot is deposited on TiO₂-coated quartz crystals using a controlled, reproducible analytical rotator. The TiO₂ film is characterized using atomic force microscopy, x-ray diffraction, and ellipsometry, whereas the soot film is described by UV-Vis spectroscopy.

Following each interval of photocatalyzed oxidation, the measured QCM frequency shifts are related to the change in adherent soot mass using the Sauerbrey equation⁴. The mass of TiO₂ and soot are varied to determine their effects on the rate of soot photooxidation. We test our series/parallel reaction mechanism to fit our data.

Figure 1: Representative visual example of soot photocatalytic oxidation on TiO2 films at (a) 0 minutes and (b) 11,000 minutes of UV illumination
(a)	(b)

______________________________________________________________________________

¹ Chin, P.; Roberts, G. W.; Ollis, D. F. Ind. Eng. Chem. Res. 2007, 46, 7598-7604.

² Mills, A.; Wang, J.; Crow, M. Chemosphere 2006, 64, 1032-1035.

³ Lee, N. C.; Choi, W. Y. J. Phys. Chem. B 2002, 106, 11818-11822.

⁴ Sauerbrey, G. Z. Phys. 1959, 155, 206-222.