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

A novel chemical exfoliation of perovskite-like KCa2Nb3O10 utilising an ami no acid intermediate is described. At first, amino acid intercalated layere d perovskite is prepared by ion-exchange reaction between the interlayer pr otons in HCa2Nb3O10 and cationic aminoundecanoic acid (H3N+(CH2)(10)COOH; A UA) under an acidic aqueous solution (pH ca. 3). Upon intercalation, the ba sal spacing of HCa2Nb3O10 expands from 14.7 Angstrom to 30.4 Angstrom to fo rm a paraffin-like monolayer arrangement of interlayered AUA molecules betw een 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 repulsiv e interaction induced by deprotonation of the carboxylic groups in the inte rlayered amino acid molecules with NaOH titration. This argument is support ed by a gradual decrease in the X-ray intensities of (00l) reflections upon base titration. The base titration curve and the zeta (zeta) potential mea surement as a function of pH suggest that the intralayer deprotonation of c arboxylic 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 bu lk oxide layers into individual monolayers. Atomic force microscopy (AFM) a nd scanning electron microscopy (SEM) observations reveal the formation of two or three elementary layers through the lattice exfoliation.