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International Journal of Photoenergy
Volume 6, Issue 2, Pages 73-80

Photocatalytic degradation of natural organic matter: Kinetic considerations and light intensity dependence

Bogazici University, Institute of Environmental Sciences, Bebek, Istanbul 34342, Turkey

Copyright © 2004 Hindawi Publishing Corporation. 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.


The current study was conducted to investigate the photocatalytic degradation kinetics of humic acid at different light intensities using commercial TiO2 powders. The pseudo first order kinetic model and Langmuir-Hinshelwood (L-H) rate equation in modified forms were used to compare the photocatalytic activities of TiO2 materials as a function of light intensity. Under constant irradiation conditions, the pseudo first order reaction rates as well as L-H rates were found to be decreasing in the following trend; Degussa P-25, Millennium PC-500 and Millennium PC-100. The pseudo first order rate constants showed the same decreasing trend as the pseudo first order reaction rates while L-H rate constants exhibited a light intensity related change in the ordering of the photocatalysts. At the lowest light intensity, L-H rate constants decreased as follows: Millennium PC-500 > Millennium PC-100 > Degussa P-25. However, increasing the light intensity changed the order to; Millennium PC-100 > Millennium PC-500 > Degussa P-25 revealing the significance of the L-H adsorption constant. Under constant irradiation conditions, ionic strength dependent changes in the structure of humic acid did not alter degradation efficiency trend of the photocatalyst specimens and they were ordered such as; Degussa P-25 > Millennium PC-500 > Hombikat UV-100 > Millennium PC-100 > Merck. The results presented in this research also confirmed the effectiveness of Degussa P-25 as a photocatalyst for the degradation of humic acid.