Adsorption of Eu(III) onto TiO2: effect of pH, concentration, ionic strength and soil fulvic acid.

The effects of pH, initial Eu(III) concentration, ionic strength and fulvic acid (FA) on the adsorption of Eu(III) on TiO2 are investigated by using batch techniques. The results indicate that the presence of FA strongly enhances the adsorption of Eu(III) on TiO2 at low pH values. Besides, the adsorption of Eu(III) on TiO2 is significantly dependent on pH values and independent of ionic strength. The adsorption of Eu(III) on TiO2 is attributed to inner-sphere surface complexation. The diffuse layer model (DLM) is applied to simulate the adsorption data, and fits the experimental data well with the aid of FITEQL 3.2. X-ray photoelectron spectroscopy (XPS) is performed to study the species of Eu(III) adsorbed on the surfaces of TiO2/FA–TiO2 hybrids at a molecular level, which suggest that FA act as “bridge” between Eu(III) and TiO2 particles to enhance the ability to adsorb Eu(III) in solution.