Biomimetic Synthesis of Nacrelike Faceted Mesocrystals of ZnO-Gelatin Composite

A fabrication of ZnO hierarchical mesocrystal was achieved by a biomimetic method using gelatin as structure-directing agent. It was found that the ZnO-gelatin microcrystal with well-defined hexagonal twin plate shape is built by the stacking of nanoplates. The irregularly edged nanoplates can adjust themselves to each other throughout the microcrystal, resulting in a roughly hexagonal edge. Selected area electron diffraction (SAED) analysis of the ZnO-gelatin microcrystal demonstrates that all the stacked nanoplates are aligned and oriented to form a single-crystal structure with hexagonal symmetry. The hierarchical structure of ZnO was found to resemble that of naturally occurring nacre. Similar to nacreous architecture, the nanoplate of ZnO was constructed from the oriented attachment of ZnO nanoparticles. More importantly, the lattices of the stacked nanoplates are aligned through mineral bridges between neighboring plates. A mechanism scheme is proposed for the formation of the gelatin-ZnO hybrid hierarchical structure. The preserved hexagonal shape of the mesocrystal structure consequently results in a whispering gallery mode (WGM) of optical emission where light was confined in the hexagons by total internal reflection. The observation of WGM mode emission in the ZnO hexagon structure shows promises for nanoscale fabrication of optoelectronic devices.