An investigation of the photocatalytic efficiencies of TiO2 powders on the decolourisation of humic acids

Photocatalytic efficiencies of two commercial titania brands, Degussa P-25 and Hombikat UV-100 were discussed in relation to the degradation of humic acid in aqueous solutions. Decolourisation rate of humic acid (Colour(436) m(-1)) for Degussa P-25 was found to be higher than the rate achieved by using Hombikat UV-100 specimen, both in terms of pseudo-first-order and Langmuir-Hinshelwood kinetics. The adsorption isotherms exhibited different trends and the application of the Freundlich adsorption model revealed K-F values 0.549 for Degussa P-25, and 0.293 for Hombikat UV-100 indicating higher adsorption capacity of Degussa P-25 for humic acid under neutral pH conditions. This observation was also consistent with the intrinsic photocatalytic activities calculated as 0.196 m(-1) min(-1) m(-2) for Degussa P-25 and 0.0269 m(-1) min(-1) m(-2) for Hombikat UV-100, The higher surface area of Hombikat UV-100 did not render higher adsorption capacity values leading to higher degradation rates. (C) 2002 Elsevier Science B.V. All rights reserved.