Key role of common anions on the photocatalytic degradation profiles of the molecular size fractions of humic acids

Humic acids are the most abundant components of the colloidal and dissolved fraction of natural organic matter (NOM) and widely known to be representatives of NOM behavior in the aquatic environment.The objective of this study was to investigate the influence of common anions on the photocatalytic degradation of humic acid and its different molecular size fractions. A representative range of anions were added to humic acid to simulate diverse characteristics of surface water. Induced effects on the removal of the target organic compound were studied. With the aim of assessing the photochemical processes under irradiation conditions, the photocatalytic removal efficiency of humic acid was determined taking into account the major background factors. The results revealed that some specific UV–vis parameters agreed well with the information provided by fluorescence spectroscopy. Despite the complex nature of humic acids in the presence of a solution matrix, the spectroscopic parameters could be regarded as indicators for the photocatalytic removal of humic acid and its molecular size fractions. Depending on the presence of low and high anion matrix, different kinetic model parameters were attained for the photocatalytic removal of the molecular size fractions of humic acid. The photocatalytic degradation rates could be expressed by the half-life values ranging from 20 min to 133 min.

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► Effect of anions on photocatalytic oxidation of humic acid molecular size fractions.
► Inhibitory effect of increasing anion concentration on the removal of humic acid.
► Spectroscopic parameters as indicators of photocatalytic removal of humic acid.