Abstract
The current study was conducted to investigate the photocatalytic degradation kinetics of humic acid at different light intensities using commercialTiO2powders. The pseudo first order kinetic model and Langmuir-Hinshelwood (L-H) rate equation in modified forms were used to compare the photocatalytic activities ofTiO2materials 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.
Highlights
Typical surface waters contain natural organic matter (NOM) a large fraction of which is humic material being negatively charged due to the dissociation of carboxylic acid and hydroxy functional groups
The dependence of the kinetic parameters on the incident light intensity and the photocatalytic activities of TiO2 materials were compared in terms of pseudo first order and Langmuir-Hinshelwood kinetic models
Different types of commercial TiO2 powders namely; Degussa P-25, Hombikat UV-100, Millennium PC-500, Millennium PC-100 and Merck were used as the photocatalyst specimens for the degradation of humic acid
Summary
Typical surface waters contain natural organic matter (NOM) a large fraction of which is humic material being negatively charged due to the dissociation of carboxylic acid and hydroxy functional groups. The acid insoluble fraction of humic material known as humic acids are the most important sunlight absorbers in natural waters that can photosensitize the oxidation of certain aquatic pollutants and biologically important substances. They constitute the major precursors of carcinogenic disinfection by-products that are produced during chlorination. Energized electrons and holes can either recombine, dissipating energy or be available for redox reactions with electron donor or acceptor species adsorbed on the semiconductor surface. A series of oxidation/reduction processes involving species such as O2, H2O2, O2− etc. may lead to complete degradation of organic compound to CO2 and inorganic ions [1, 2]
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