Formation and Scrolling Behavior of Metal Fluoride and Oxyfluoride Nanosheets

Abstract

We report 1–2 unit-cell-thick CaF2 nanosheets, which can be converted topochemically into LaF3–2xOx nanosheets that scroll spontaneously. The formation of CaF2 nanosheets is achieved through interlayer confinement and templating within CaSi2 during reaction with aqueous HF. The structure and morphology of these nanosheets are characterized by HRTEM, AFM, and powder XRD. Solid-state MAS and solution 19F NMR spectroscopies provide further information about interstitial fluoride sites within CaF2 nanosheets as well as help identify side products of the CaSi2 + HF reaction. CaF2 nanosheets react with lanthanide salts at room temperature to yield nanostructured hexagonal LnF3 (Ln = Ce, Pr, Nd, Sm, Eu), orthorhombic LnF3 (Ln = Gd, Dy, Ho, Er, Yb), and cubic YbF3–x products. Furthermore, the reaction of CaF2 nanosheets with lanthanum salts is unique in producing LaF3–2xOx. The evidence for this composition includes powder XRD, EDS, XPS, and 19F NMR data. The structure of LaF3–2xOx differs from hexagonal LaF3 onl...