Facile Exfoliation of Layered Titanoniobate (KTiNbO5) into Colloidal Nanosheets

We herein describe a soft-chemical route to exfoliation of layered semiconductive titanoniobate (KTiNbO5) into individual oxide nanosheets. The protonic layered titanoniobate (HTiNbO5), derived from KTiNbO5, is reacted with zwitterionic aminoundecanoic acid (H2N(CH2)10COOH; AUA) to replace the interlayer H+ ions with AUA molecules in an acidic aqueous solution (pH approximately 3). On intercalating amino acid molecules into titanoniobate layers, the basal spacing expands from 8.5 angstroms to 23.7 angstroms. Further expansion of the layers is achieved by a host-guest repulsive interaction via the interlayer deprotonation of the carboxylic groups of amino acid molecules in a basic aqueous solution. The exfoliated oxide nanosheets exhibit remarkable colloidal stability in aqueous solution with a significant spectral blue shift in UV optical absorption spectra. Moreover, atomic force microscopic (AFM) and scanning electron microscopic (SEM) observations directly confirm the delamination of parent microcrystals.