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International Journal of Photoenergy
Volume 2006, Article ID 85927, 7 pages
http://dx.doi.org/10.1155/IJP/2006/85927

Aqueous photocatalytic oxidation of lignin and humic acids with supported TiO2

1Department of Chemical Engineering, Tallinn University of Technology, Ehitajate tee 5, Tallinn 19086, Estonia
2Department of Chemical Technology, Lappeenranta University of Technology, P.O. Box 20, Lappeenranta 53851, Finland

Received 19 February 2006; Accepted 19 February 2006

Copyright © 2006 Elina Portjanskaja et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The photocatalytic oxidation (PCO) of UV-irradiated aqueous solutions containing humic acids and lignin was studied. The photocatalyst TiO2 was attached to buoyant hollow glass microspheres and glass plates. A maximum oxidation efficiency as low as 1.1 and 2.54 mg W1h1 for humic acids and lignin, respectively, was achieved in neutral and alkaline media with 25 gm2 of the buoyant catalyst. In acidic media, efficiency was even lower. The photocatalytic efficiency with the photocatalyst attached to glass plates was about 3 to 4 times higher than that for the buoyant catalyst. Ferrous ions added to acidic solutions did not increase the rate of PCO of humic acids. However the addition of Fe2+ ions, up to 0.05 mM, to the lignin solution leads to a dramatic increase, about 25%, in PCO efficiency. A further increase in ferrous ion concentration results in a decrease in the PCO efficiency of lignin. Proceeding most likely by a radical mechanism, the efficiency of PCO of humic acids did not benefit from an excessive presence of hydroxyl radical promoters, such as hydrogen peroxide, although the reaction rate increased. However, PCO of lignin in the acidic medium, where OH.-radical formation is suppressed, benefited from the introduction of hydrogen peroxide due to promoted radical formation.