A COMPARATIVE APPROACH TO SURFACE INTERACTIONS BETWEEN MOLECULAR SIZE FRACTIONS OF HUMIC ACID AND ANION DOPED TITANIA BINARY SYSTEM

摘要

In this study, surface interactions between different molecular size fractions of humic acid (0.45 urn filtered fraction, 100 kDa fraction and 30 kDa fraction) and two commercially available bare and anion doped titanium dioxide (TiO_2) suspensions (Degussa P-25 and Hombikat UV-100) in the range of 0.1-1.0 mg mL~(-1) were comparatively evaluated.Adsorption properties of humic acid (HA) and its molecular size fractions onto bare TiO_2 and anion doped TiO_2 specimens were evaluated and compared in terms of UV-vis spectroscopic parameters i.e. color forming moieties (Colore) and UV absorbing centers (UV_(365), UV_(280) and UV_(254)) and respective specific UV-vis parameters (SCoA, SUVA_(365), SUVA_(280), and SUVA_(254)) and also fluorescence spectroscopy in emission and synchronous scan modes as well as dissolved organic carbon (DOC, mgL~(-1)). In equilibrium studies, the data obtained by adsorption experiments were evaluated by Freundlich, Langmuir and Dubinin-Radushkevich isotherm models.Freundlich, Langmuir and Dubinin-Radushkevich isotherm model parameters of DOC for all of molecular size fractions of HA following adsorption onto bare and anion doped TiO_2 P-25 and UV-100 specimens displayed significantly differences. The reason could be attributed to the role of the functional groups (fluorophoric and chromophoric groups) existing in the diverse molecular size fractions of HA. Assessment of the consequences obtained from different molecular size fractions of HA pointed out remarkable diversities both with respect to the type of dopant and also to the morphological character of TiO_2 specimens.