TiO2-assisted photocatalytic degradation of humic acids: effect of copper ions

The present study investigated the removal efficiency of aqueous humic acid solutions by TiO2 photocatalytic degradation in the presence of Cu(II) species. The pseudo-first-order kinetics revealed rate constants as 9.87 x 10(-3), 7.19 x 10(-3), 3.81 x 10(-3) min(-1) for Color(436), UV254 and TOC, respectively. Comparatively, lower rate constants were attained with respect to photocatalytic degradation of humic acid. Considering the source-dependent diverse chemical and spectral characteristics of NOM, a particular interaction would be expected for humic acid with Cu(II) species (0.1mgL(-1)). The presence of copper ions significantly altered the photocatalytic degradation kinetics of humic acids in relation to the concentration effects of humic acid as expressed by spectroscopic parameters and TOC. Batch equilibrium adsorption experiments revealed a distinct Langmuirian-type adsorptive behavior of humic acid onto TiO2 both in terms of UV254 and Color(436) and a C-type adsorption isotherm was attained for TOC. K-F values displayed an inconsistent effect of Cu(II) species, while adsorption intensity factor 1/n < 1 denoted a prevailing favorable type of adsorption for Color(436) and UV254. Because of the role of intra-and intermolecular interactions between copper ions and humic molecular size fractions, spectroscopic techniques were also employed for the assessment of the adsorption as well as photocatalytic degradation efficiencies.