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

A detailed study on the structural deformation of trititanate nanofibers after the adsorption of divalent strontium (Sr) and barium (Ba) cations was 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 Ba 2+ and Sr 2+ 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 TiO 6 octahedra in Na 2 Ti 3 O 7 are more regular. These results suggest that the active sodium (Na + ) cations in Na 2 Ti 3 O 7 should be located at the corner of the TiO 6 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.