Exfoliated two-dimensional nanosheets for self-assembly of new nanostructures

The spontaneous exfoliation of some layered clay minerals upon the uptake of water molecules in the interlayers have been well known for ages. Apart from these “old” examples, subject to appropriate ion-exchange and infinite swelling process, namely exfoliation or delamination, a large number of layered compounds including transition metal oxides, metal phosphates, layered double hydroxides, metal chalcogenides and graphite oxide can also undergo exfoliation to produce individual single sheets, so-called nanosheets. The resultant sheets can be considered as a new type of nano-scaled materials due to their unique features such as single-crystallinity, well-defined composition, unilamellar shape with extremely small thickness of ca. 1 nm and lateral sizes up to micrometers, surface charges and colloidal nature. Such nanosheets usually exhibit novel physiochemical properties that are rarely attained in their bulk counterparts, evidenced by unique characteristics of some well-characterized nanosheets, such as graphene. Using the exfoliated two dimensional nanosheets as building blocks, a variety of new nanostructures including polymernanosheet composites, multilayered ultrathin films, core-shell/hollow shells, tubular low-dimensional structures and restacked/pillared nanoporous materials can be rationally assembled, which have found applications broadly ranging from ionexchange and separation to catalysis and photocatalysis, from electrochemistry and sensing to mechanics and electronics