Assessment of molecular size distribution effects on the nonselective oxidation of trace metal humic acid binary system

Abstract

The objective of this research to investigate the effects of zinc ions on the nonselective photocatalytic degradation of humic acid in aqueous medium. The photocatalytic oxidation of humic was carried out using TiO2 Degussa P-25 as the photocatalyst. The degradation kinetics was assessed based on pseudo first order. The complex interactions between the surface properties of titanium dioxide and the molecular size dependent fractions of the humic acid were studied. The role of the metal ion complexation as expressed by the “binary system effect” on the photocatalytic degradation efficiency of humic acids with respect to molecular size fractions was deduced. The experiments were conducted with different molecular size fractions such as raw, 0.45 μm filtered fraction, 100 kDa fraction and 30 kDa fraction of Aldrich humic acid solution in the presence and the absence of zinc ion The molecular and structural characteristics of the humic acid molecule relative to changes during photocatalytic oxidation were evaluated on a comparative basis by UV-vis and fluorescence spectroscopy. The declining trend of the specified UV-vis parameters, the related changes in the fluorescence spectra indicated the oxidative degradation of humic acid. As confirmed by the spectroscopic evaluation of the molecular size distribution, photocatalytic degradation of humic acid led to the formation of lower molecular size and higher UV-absorbing compounds.|Keywords: Humic Acid, Photocatalytic degradation, Adsorption, Molecular Size Fraction, Zinc.