Iron(III)-doped Q-sized TiO_2 coatings in a fiber-optic cable photochemical reactor

Abstract

The photochemical quantum efficiencies and oxidation performance of iron(III)-doped quantum-sized TiO_2 (Fe/Q-TiO_2), Degussa P25 (P25), and hybrid Fe/Q-TiO_2/P25 photocatalytic coatings are investigated using an optical fiber bundled array reactor. Fe/Q-TiO_2 coatings made from hydrosols of varying Fe/Q-TiO_2 content, 5–20 wt.%, a 13 wt.% P25 coating, and a hybrid, layered Fe/Q-TiO_2/P25 (5/13 wt.%) coating are tested. The light absorption efficiencies of the Fe/Q-TiO_2 coatings are inferior to the P25 coating, absorbing a maximum of only 80% of the input light compared with greater than 95% for P25 and 90% for the hybrid coating. The Fe/Q-TiO_2 coatings are found to increase the linear light transmission in a single optical fiber relative to P25 coated fibers by a factor of two owing to a reduced interfacial surface coverage of the photocatalyst particles on the quartz fiber. The hybrid coating does not significantly enhance linear light transmission. Slurry-phase photoefficiencies for the photooxidation of 4-chlorophenol for the Fe/Q-TiO_2 photocatalyst are found to be significantly lower than those measured for P25, φFe/Q-TiO_2 = 0.002 vs.φ_(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-TiO_2 coating. Thus, we are unable to investigate the effect of increased light transmission on the photoefficiency of the system. Initial reaction rates for the photooxidation of 4-chlorophenol range from 2.0 to 4.5 μM h^(−1) generally increasing with increasing hydrosol Fe/Q-TiO2 content and an average relative quantum efficiency of φ_(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 μM h^(−1), and φFe/_(Q-TiO2/P25) = 0.011 and 20.4 μM h^(−1) and φ_(P25) = 0.012 for the hybrid and P25 coatings, respectively.