Growth Mechanism of Sea Urchin ZnO Nanostructures in Aqueous Solutions and Their Photocatalytic Activity for the Degradation of Organic Dyes.

This work reports the development of a fast and simple route for the synthesis of ZnO sea urchin (SU) nanostructures by the formation and assembly of ZnO nanorods under favorable growth conditions in an aqueous solution. The thermal treatment of a basic zinc acetate solution in ethanol results in the formation of aggregated seed clusters consisting of small ZnO nanorods, which were then grown in a precursor solution containing Zn(NO)·6HO and hexamethylenetetramine to assemble the SU structures from the anisotropic ZnO nanorods on the surface of the seed clusters. Each ZnO nanoparticle in the aggregated seed clusters grew sequentially into a ZnO nanorod, and the nanorods were concentric to the core of the clusters yielding the unique SU-like shape. In the presence of a capping agent such as cetyl trimethyl ammonium bromide (CTAB), the aggregated seed clusters were not formed, and the growth of the CTAB-capped ZnO nanorods resulted in separated rods with average aspect ratios of ∼10. The SU ZnO nanostructures exhibit a hexagonal wurtzite crystal structure and higher specific surface area (26.9 m/g) than the CTAB-capped nanorods (17.7 m/g). The SU ZnO nanostructures show superior photocatalytic efficiency for the degradation of three common organic dyes compared to the ZnO nanorods. The removal efficiencies of indigo carmine, methylene blue, and rhodamine B by the SU nanostructures were 99, 86, and 96%, respectively, after 1 h of UV irradiation. Therefore, the ZnO SU structures have the potential to be a versatile photocatalyst for the photodegradation of organic dyes in industrial wastewater.