Organic molecule-assisted hydrothermal self-assembly of size-controlled tubular ZnO nanostructures

Tubular ZnO nanostructures have been synthesized by hydrothermal self-assembly of zinc ions at the interface of organic molecules and solution. The morphologies and structures of the products were investigated by XRD, SEM, and TEM. Surfactants, cationic cetyltrimethylammonium bromide (CTAB), and the neutral triblock copolymer of polyethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (P123) were found to be suitable organic molecules for the assembly of layered zinc species-surfactant hybrids that can be exfoliated into single sheets. These sheet-like intermediates roll to form tubular ZnO nanostructures due to the heat stress and the crystallization of ZnO sheets. The size of tubular ZnO is determined by the type of surfactants, the concentration of surfactant, and the zinc species/surfactant molar ratio. Microtubes and nanotubes were prepared by using the organic molecules of CTAB and P123, respectively. All tubular ZnO nanostructures were found coexisting with the single sheet, layered sheets, and half-tube/half-sheet structures, indicating the rolling of sheet-like intermediates to form the tubular ZnO nanostructures. In comparison to the products synthesized in pure water, the interface assembly between organic molecules and inorganic species is the underlying mechanism for the morphologic formation and structural evolution of tubular-like ZnO nanostructures. All diffraction peaks of the ZnO products are well indexed to the hexagonal phase (space group P6₃mc) ZnO.