Adsorption of Eu(III) on a heterogeneous surface studied by Time-Resolved Laser Fluorescence Microscopy (TRLFM)

Ishida, Keisuke*; Kimura, Takaumi ; Saito, Takumi*; Tanaka, Satoru*

Time-Resolved Laser Fluorescence Microscopy (TRLFM) is a useful tool to simultaneously investigate the intensity, location, types and surrounding chemical environment of a fluorophore. In this study, we demonstrated the applicability of TRLFM for the adsorption of Eu(III) on a natural heterogeneous surface. Different chemical species of Eu(III) were observed on the Makabe granite surface and its constituents (biotite, plagioclase, potassium feldspar and quartz). Eu(III) heterogeneously adsorbed on biotite, plagioclase and quartz and homogeneously on potassium feldspar. The histograms of the fluorescence decay rates of adsorbed Eu(III) revealed the presence of single specie of Eu(III) on biotite and two common species on plagioclase and potassium feldspar. The adsorption of Eu(III) on Makabe granite surface was highly heterogeneous. The TRLFM measurements of different regions of the granite surface turned into the finding of Eu(III) with different fluorescence decay rates. Comparing with fluorescence decay histograms of the mineral constituents, Eu(III) clearly adsorbed on the feldspar family, plagioclase and potassium feldspar. It was also found that Eu(III) adsorbed as an outer-sphere complex and on an altered mineral, possibly smectite resulting from the weathering plagioclase.