Titanium dioxide-mediated photocatalytic degradation of humic acid under natural sunlight.
ABSTRACT In this article, photocatalytic degradation of humic acid, a predominant type of natural organic matter present in ground and surface waters, was conducted using a commercial titanium dioxide catalyst under natural sunlight irradiation in a batch photoreactor. Various parameters, such as photocatalyst loading, pH value, irradiation intensity, initial concentration, and illumination time, had a significant influence on humic acid removal. The adsorption isotherm of TiO2 dosage fit to Langmuir's isotherm equation well, and the reaction kinetics of initial dissolved organic carbon (DOC) concentration increased with the increase of TiO2 dosage but decreased with the increase of initial DOC. The mineralization of humic acid revealed that the large molecular weight organics with aromatic and hydrophobic properties were removed, while the most persistent components were the shortest UV-absorbing and hydrophilic low-molecular-weight compounds. This study indicates that the solar/ TiO2 photocatalytic degradation is a promising process for humic acid removal from water.
- SourceAvailable from: Ceyda Uyguner Demirel[Show abstract] [Hide abstract]
ABSTRACT: 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 (Colour436, 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 KF 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.Journal of Photochemistry and Photobiology A Chemistry 05/2002; · 2.29 Impact Factor
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ABSTRACT: Adsorption of natural organic matter (NOM) onto seven activated carbons with a wide range of surface properties was studied at high and low ionic strength over a range of pH values. From adsorption isotherm studies it was found that, for six of seven carbons, at low surface concentrations, increased ionic strength decreased NOM adsorption. As the surface concentration increased, the adsorption isotherms converged and intersected, after which the addition of salt resulted in increased adsorption. This "crossover point" marked a change in the adsorption mechanism from the "screening reduced" to the "screening enhanced" adsorption regimes. The adsorption mechanisms are extremely complicated and appear attributable to various factors, including electrostatic forces, pore volume distribution, and chemical interactions between the NOM and the surface functionalities on the carbon surfaces. Copyright 1999 Academic Press.Journal of Colloid and Interface Science 03/1999; 210(2):271-280. · 3.55 Impact Factor
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ABSTRACT: The presence of humic acid may change the way phosphate is absorbed or stabilized by soil and how it influences the growth of plants. The binding of phosphate with the humic substance requires bridging between phosphate ions and humic acid by metal ions, such as aluminum or iron ions. The bridging reaction can take place in peat and allophane soil under acidic conditions, altering the effectiveness of the phosphate in soil. Whether ternary phosphate-metal-HA complexes are actually formed has not yet been verified. This study considers variation in fluorescence intensity (FI) under various coagulation conditions to assess the mechanism by which humic acids and phosphate react with aluminum ions. A bond between the functional group of the humic acid and the electron-releasing group of the phosphate will enhance the florescent intensity of humic acids. Consequently the removal efficiency of humic acid, measured by florescence, declines as the phosphate concentration increases at low pH. This observation suggests that at low coagulation pH, the positively charged aluminum species can be used to bridge between the phosphate ion and the humic acid molecules.Journal of Colloid and Interface Science 05/2004; 272(1):153-7. · 3.55 Impact Factor