Abstract
To contribute to the understanding of Eu(III) interaction preperties on hydrous alumina particles in the absence and presence of fulvic acid (FA), the complexation properties of Eu(III) with hydrous alumina, FA and FA-alumina hybrids are studied by batch and time-resolved laser fluorescence spectroscopy (TRLFS) techniques. The continuous increase in the fluorescence lifetime of Eu-alumina and Eu-FA with increasing pH indicates that the complexation is accompanied by decreasing number of hydration water in the first coordination sphere of Eu(III). Eu(III) is adsorbed onto alumina particles as outer-sphere surface complexes of ae(Al-O)-Eu center dot (OH)center dot 7H(2)O and ae(Al-O)-Eu center dot 6H(2)O at low pH values, and as inner-sphere surface complexes as ae(Al-O)(2)-Eu+center dot 4H(2)O at high pH. In FA solution, Eu(III) forms complexes with FA as (COO)(2)Eu+(H2O) (x) and the hydration water number in the first coordination sphere decreases with pH increasing. The formation of aeCOO-Eu-(O-Alae)center dot 4H(2)O is observed on FA-alumina hybrids, suggesting the formation of strong inner-sphere surface complexes in the presence of FA. The surface complexes are also characterized by their emission spectra [the ratio of emission intensities of (5) D (0)->(7) F (1) (lambda=594 nm) and (5) D (0)->(7) F (2) (lambda=619 nm) transitions] and their fluorescence lifetime. The findings is important to understand the contribution of FA in the complexation properties of Eu(III) on FA-alumina hybrids that the clarification of the environmental behavior of humic substances is necessary to understand fully the behavior of Eu(III), or its analogue trivalent lanthanide and actinide ions in natural environment.