A Raman spectroscopic study on the active site of sodium cations in the structure of Na2Ti3O7 during the adsorption of Sr2+ and Ba2+ cations

Abstract

A detailed study on the structural deformation of trititanate nanofibers after the adsorption of divalent strontium (Sr) and barium (Ba) cationswas conducted by using Raman spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the Raman bands at 309 cm−1 corresponding to very long Ti–O bonds (2.2 Å) and at 883 cm−1 corresponding to the very short Ti–O bonds (1.7 Å) decreased in intensity after the adsorption of Ba2+ and Sr2+ cations. Additionally, the band at 922 cm−1 corresponding to an intermediate length Ti–O bond was observed to weaken with the adsorption of divalent cations, indicating that the TiO6 octahedra in Na2Ti3O7 aremore regular. These results suggest that the active sodium (Na+) cations in Na2Ti3O7 should be located at the corner of the TiO6 octahedral slabs, i.e. the plane (003). This was further confirmed by a large decrease of diffraction intensity of the plane (003) observed in the XRD pattern.