IRON(III)-DOPED Q-SIZED TIO2 COATINGS IN A FIBEROPTIC CABLE PHOTOCHEMICAL REACTOR

The photochemical quantum efficiencies and oxidation performance of ir on(III)-doped quantum-sized TiO2 (Fe/Q-TiO2), Degussa P25 (P25), and h ybrid Fe/Q-TiO2/P25 photocatalytic coatings are investigated using an optical fiber bundled array reactor. Fe/Q-TiO2 coatings made from hydr osols of varying Fe/Q-TiO2 content, 5-20 wt.%, a 13 wt.% P25 coating, and a hybrid, layered Fe/Q-TiO2/P25 (5/13 wt.%) coating are tested. Th e light absorption efficiencies of the Fe/Q-TiO2 coatings are inferior to the P25 coating, absorbing a maximum of only 80% of the input ligh t compared with greater than 95% for P25 and 90% for the hybrid coatin g. The Fe/Q-TiO2 coatings are found to increase the linear light trans mission in a single optical fiber relative to P25 coated fibers by a f actor of two owing to a reduced interfacial surface coverage of the ph otocatalyst particles on the quartz fiber. The hybrid coating does not significantly enhance linear light transmission. Slurry-phase photoef ficiencies for the photooxidation of 4-chlorophenol for the Fe/Q-TiO2 photocatalyst are found to be significantly lower than those measured for P25, phi(Fe/Q-TiO2) = 0.002 vs. phi(P25) = 0.012. In addition, the length of the coated fiber-bundle used in our reactor is insufficient to capitalize on the increased light transmission for the Fe/Q-TiO2 c oating. Thus, we are unable to investigate the effect of increased lig ht transmission on the photoefficiency of the system. Initial reaction rates for the photooxidation of 4-chlorophenol range from 2.0 to 4.5 mu M h(-1) generally increasing with increasing hydrosol Fe/Q-TiO2 con tent and an average relative quantum efficiency of phi(Fe/Q-TiO2) = 0. 004 +/- 0.001 is observed. These values are significantly low compared with initial rates and relative quantum efficiencies of 18.0 mu M h(- 1), and phi(Fe/Q-TiO2/P25) = 0.011 and 20.4 mu M h(-1) and phi(P25) = 0.012 for the hybrid and P25 coatings, respectively. (C) 1997 Elsevier Science S.A.