Surfactant-assisted alignment of ZnO nanocrystals to superstructures

Self-organization of ZnO nanoparticles into various superstructures (sheet, platelet, ring) has been achieved with the assistance of micelles formed by surfactant cetyltrimethylammonium bromide (CTAB) under one-pot condition. The CTAB-modified zinc hydroxy double salt (Zn-HDS) mesocrystals act as intermediates to form ZnO hexagonal superstructures at temperatures as low as 50 degrees C. The decomposition temperature of Zn-HDS mesocrystals is much lower than that of the corresponding bulk crystals because the organic additive CTAB effectively decreases the degree of crystallinity. Taking advantage of temperature-induced phase transformation of micelles, two-stage self-organization can form ZnO platelets and ring mesocrystals, that is, ZnO ellipsoidal superstructures formed through vertical attachment on (0001) facets of basic units can further assemble to form ZnO platelets and rings through vertical attachment on (0001) facets of ZnO ellipsoidal superstructures. The structural transformation of micelles as shape templates can offer a new route for self-assembly of nonspherical colloids into three-dimensional photonic crystals. ZnO sheet, ring, and platelet mesocrystals with a high population of polar Zn-(0001) plane are expected to have high photocatalytic activity.