Soft-Chemical Exfoliation
of RbSrNb<sub>2</sub>O<sub>6</sub>F into Homogeneously Unilamellar
Oxyfluoride Nanosheets
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Abstract
Interlayer Rb<sup>+</sup> of the perovskite-type layered
oxyfluoride RbSrNb<sub>2</sub>O<sub>6</sub>F was ion-exchanged with
H<sup>+</sup>, and the protonated phase was reacted with aqueous solution
of tetrabutylammonium hydroxide to exfoliate it into nanosheets. The
resulting nanosheet suspension exhibits Tyndall scattering of a laser
beam, indicating its colloidal nature. Elemental composition of the
nanosheet was estimated as Sr<sub>0.98</sub>Nb<sub>2</sub>O<sub>6</sub>F<sub>0.97</sub><sup>δ−</sup>, which was quite close
to that of the layer unit of the precursor. The homogeneously unilamellar
nature of this nanosheet was confirmed by atomic force and transmission
electron microscopy observations and X-ray scattering results. The
optical absorption edge of the nanosheet suspension was observed around
at 293 nm, and two well-defined peaks with their maxima at 229 and
278 nm were observed. Furthermore, the aqueous suspension of the nanosheet
exhibits fluorescence emission in the UV-blue region. These properties
of the oxyfluoride nanosheets are quite different from those of its
oxide analogues without F<sup>–</sup>, such as LnNb<sub>2</sub>O<sub>7</sub><sup>–</sup> nanosheets (Ln = La<sup>3+</sup>, Eu<sup>3+</sup>, Sm<sup>3+</sup>), suggesting that anion-site replacement
of oxide nanosheets can be utilized to optimize or induce various
properties
