Exfoliation of layered perovskite, KCa2Nb3O10, into colloidal nanosheets by a novel chemical process

A novel chemical exfoliation of perovskite-like KCa2Nb3O10 utilising an amino acid intermediate is described. At first, amino acid intercalated layered perovskite is prepared by ion-exchange reaction between the interlayer protons in HCa2Nb3O10 and cationic aminoundecanoic acid (H3N+(CH2)(10)COOH; AUA) under an acidic aqueous solution (pH ca. 3). Upon intercalation, the basal spacing of HCa2Nb3O10 expands from 14.7 Angstrom to 30.4 Angstrom to form a paraffin-like monolayer arrangement of interlayered AUA molecules between the perovskite slabs. Subsequent infinite expansion of the oxide layers, which eventually leads to the exfoliation of perovskite slabs (Ca2Nb3O10) into elementary oxide nanosheets, is accomplished by a host-guest repulsive interaction induced by deprotonation of the carboxylic groups in the interlayered amino acid molecules with NaOH titration. This argument is supported by a gradual decrease in the X-ray intensities of (00l) reflections upon base titration. The base titration curve and the zeta (zeta) potential measurement as a function of pH suggest that the intralayer deprotonation of carboxylic groups occurs rapidly in the pH range 8-9. A significant spectral blue shift for the colloidal particles compared to the pristine HCa2Nb3O10 in the UV-vis absorption spectra also substantiates the delamination of bulk oxide layers into individual monolayers. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) observations reveal the formation of two or three elementary layers through the lattice exfoliation.