Inorganic Janus nanosheets were successfully prepared using the difference in reactivity between interlayers I and II of layered hexaniobate K4Nb6O17·3H2O. Janus nanosheets exhibit the highest anisotropy among Janus compounds due to their morphology. It is therefore important to prepare Janus nanosheets with stable shapes in various solvents, robust chemical bonds between nanosheets and fuctional groups and high versatility due to surface functional groups. K4Nb6O17·3H2O, which possesses two types of interlayers and two types of organophosphonic acids that react with metal oxides to form robust covalent bonds, was employed to prepare Janus nanosheets for this study. Interlayer I was modified by octadecylphosphonic acid, followed by modification by carboxypropylphosphonic acid mainly at interlayer II. Preparation of Janus nanosheets with two organophosphonate moieties was confirmed by 31P MAS NMR. After these regioselective and sequential modifications, the products were exfoliated into single-layered nanosheets in THF. Two types of derivatives with different repeating distances were recovered from a dispersion containing nanosheets exfoliated by different processes, centrifugation, and solvent evaporation. AFM analysis of the exfoliated nanosheets revealed that the products were Janus compounds. There are high expectations for application of these types of Janus nanosheets in various fields and for design of various Janus nanosheets using this preparation method.
Part of the book: Functional Materials