Surface speciation of Eu³⁺ adsorbed on kaolinite by time-resolved laser fluorescence spectroscopy (TRLFS) and parallel factor analysis (PARAFAC)

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• 作者：Keisuke Ishida^a ; Takumi Saito^b ; ^{takumi@flanker.n.t.u-tokyo.ac.jp} ; Noboru Aoyagi^c ; Takaumi Kimura^c ; Ryuji Nagaishi^c ; Shinya Nagasaki^d ; Satoru Tanaka^b
• 关键词：Europium ; Kaolinite ; Adsorption ; Time-resolved laser fluorescence spectroscopy ; Parallel factor analysis ; Surface complexation
• 刊名：Journal of Colloid and Interface Science
• 出版年：2012
• 期刊代码：125_00219797
• 类别：ch
• 出版时间：15 May, 2012
• 卷：374
• 期：1
• 页码：258-266
• 文件大小：635 K

摘要

Time-resolved laser fluorescence spectroscopy (TRLFS) is an effective speciation technique for fluorescent metal ions and can be further extended by the parallel factor analysis (PARAFAC). The adsorption of Eu³⁺ on kaolinite as well as gibbsite as a reference mineral was investigated by TRLFS together with batch adsorption measurements. The PAFAFAC modeling provided the fluorescence spectra, decay lifetimes, and relative intensity profiles of three Eu³⁺ surface complexes with kaolinite; an outer-sphere (factor A) complex and two inner-sphere (factors B and C) complexes. Their intensity profiles qualitatively explained the measured adsorption of Eu³⁺. Based on the TRLFS results in varied H₂O/D₂O media, it was shown that the outer-sphere complex exhibited more rapid fluorescence decay than Eu³⁺ aquo ion, because of the energy transfer to the surface. Factor B was an inner-sphere complex, which became dominant at relatively high pH, high salt concentration and low Eu³⁺ concentration. Its spectrum and lifetime were similar to those of Eu³⁺ adsorbed on gibbsite, suggesting its occurrence on the edge face of the gibbsite layer of kaolinite. From the comparison with the spectra and lifetimes of crystalline or aqueous Eu(OH)₃, factor C was considered as a poly-nuclear surface complex of Eu³⁺ formed at relatively high Eu³⁺ concentration.