XPS, XRF, XRD, EXAFS及びNMRによるNi-イオン交換KAISiO_4中でのNi^<2+>の存在状態のキャラクタリゼーション

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Imperfectly ordered KAlSiO_4 shows a greatly increased uptake of Ni^<2+> from solution which motivated this study of the state of Ni^<2+> in Ni-exchanged KAlSiO_4 using X-ray photo-electron spectroscopy (XPS), X-ray fluorescence (XRF), powder X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) and solid state nuclear magnetic resonance spectroscopy (NMR). The imperfectly ordered KAlSiO_4 was synthesized by solid-state reaction of kaolinite with K_2CO_3 at 550℃ for 24 h. The Ni-exchanged KAlSiO_4 samples were obtained by treatment in a solution containing 10^<-3>-10^<-1>M NiCl_2 buffered with 0.5 M NaCl at 60℃. Comparison of the surface and bulk chemical compositions analyzed by XPS and XRF indicated that the Ni^<2+> sorbed on the KAlSiO_4 is largely concentrated at the surface. The XRD pattern of the Ni-exchanged KAlSiO_4 showed weak broad peaks corresponding to a phase with a layered structure and a change in the halo pattern of the KAlSiO_4. EXAFS analysis confirmed the presence of a Ni-containing layered double hydroxide (LDH; Ni_<1-y>Al_y(OH)_2X_y・nH_2O) as indicated by the interatomic Ni-Ni distance and Ni coordination number. The ^<29>Si MAS NMR showed shift and peak splitting corresponding to an increase in the degree of polymerization of the SiO_4 tetrahedra forming the framework of the tridymite-type structure and the ^<27>Al MAS NMR showed an increase of six coordinated Al in the Ni-exchanged KAlSiO_4. It is concluded, from all these results, that the Ni^<2+> in Ni-exchanged KAlSiO_4 forms a Ni-Al LDH-like phase on the surface of the KAlSiO_4. This is considered to be the main reason for the higher Ni^<2+> uptake compared with various other cations adsorbed on imperfectly ordered KAlSiO_4.
2000-11-01

XPS, XRF, XRD, EXAFS及びNMRによるNi-イオン交換KAISiO_4中でのNi^<2+>の存在状態のキャラクタリゼーション

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