A comparative study on the photocatalytic degradation of humic substances of various origins

The photocatalytic removal of model humic and fulvic acids of different origins (terrestrial and aquatic) was investigated using TiO2 Degussa P-25 as the photocatalyst. The results were presented comparatively based on pseudo-first-order and the Langmuir-Hinshelwood kinetic models. The reaction rates calculated for the UV-vis parameters follow the general trend: IHSS soil humic acid > Aldrich humic acid > IHSS humic acid > Roth humic acid > IHSS fulvic acid. However, the rate constants show differences depending on the UV-vis absorption parameters. The evaluation of the Langmuir-Hinshelwood kinetic model reveals that, in all cases, Roth humic acid has the lowest Langmuir-Hinshelwood rate, rate constant and adsorption coefficient, and the ordering of the rates follows the same trend with that of pseudo-first order. Furthermore, data related to the molecular size distribution profiles of raw and treated humic acids suggest that the photocatalytic degradation occurs irrespective of the molecular size fractions.