General Synthesis of Large Inorganic Nanosheets via 2D Confined Assembly of Nanoparticles.

Assembling nanoparticles to spatially well-defined functional nanomaterials and sophisticated architectures has been an intriguing goal for scientists. However, maintaining a long-range order of assembly to create macrostructures remains a challenge, owing to the reliance on purely interparticle interactions. Here, we present a general strategy to synthesize a class of inorganic nanosheets via a bottom-up directional freezing method. We demonstrate that, by confining a homogeneously dispersed metal-cyano colloidal suspension at the ice-water interface, followed by removal of ice crystals, large nanosheets with a lateral scale of up to several millimeters can be produced. The formation of millimeter-sized nanosheets is attributed to balanced electrostatic forces between dispersed nanoparticles, coupled with an appropriate hydrodynamic size of nanoparticles, potentially favorable lattice matching between nanoparticles and ice crystals, and the intermediate water at the ice-particle interface. The highly anisotropic growth of ice crystals can therefore guide the 2D confined assembly of nanoparticles in a long-range order, leading to well-defined 2D nanosheets. This contribution sheds light on the potential of nanoparticle assembly at larger length scales in designing families of large 2D nanoarchitectures for practical applications.