Microscale sphere assembly of ZnO nanotubes

In this paper, we report a facile method to perform microsphere organization of ZnO nanotubes. Study shows ZnO nanotubes with diameters of 80–150 nm and lengths of 1.2–2 μm were assembled into 3–4.5 μm microsphere superstructures, the significance of these assembled ZnO nanotubes is that one-dimensional anisotropic ZnO building blocks are selectively aligned into highly symmetrical three-dimensional isotropic conformations, which may promise us new types of ZnO applications. These microsphere assemblies of ZnO nanotubes have a wide visible yellow emission at 600 cm−1. The assembly mechanism was also proposed, the addition of metallic zinc species into linear poly ethylene glycol (PEG) containing ethanol and water mixed solution led to aggregation of PEG polymer coils to Zn(II)/PEG globules with a diameter of ∼500 nm, the globule turned into tube-like-structured ZnO–PEG microsphere assemblies (∼2 μm) after ultrasonic pretreatment, ZnO nanotubes were formed by the oriented attachment and Ostwald ripening of ZnO growth units onto the tube-like structures during the following hydrothermal process.