Hierarchical nanostructures of ZnO obtained by spray pyrolysis

A two step spray pyrolysis deposition method was applied in order to grow ZnO nanorod core/ZnO shell hierarchical nanostructures with various surface morphologies, such as a highly organised platelet network on the side facets of the ZnO rod and bundles of nanoneedles on the top plane of the rod. First, well-shaped ZnO nanorods with lengths of ca. 1 μm and average diameters of 150–300 nm were deposited from zinc chloride (ZnCl₂·2H₂O) aqueous solutions onto TCO/glass substrates. Then, zinc acetate (Zn(CH₃COO)₂·2H₂O) solution was pulverised over the surface of the sprayed ZnO nanorods at a growth temperature of approximately 330 °C within 6–10 min. The obtained structures were characterised by high resolution SEM, UV–VIS and XRD. To estimate the surface areas and photocatalytic ability of the bare rods and hierarchical structures, their adsorption ability and activity of photocatalytic oxidation of doxycycline were measured. It was found that the surface area of hierarchical structures comprised of a network of platelets is at least 4 times larger than that of a bare rod. The structural and morphological properties of sprayed hierarchical structures largely depend on the spraying rate of the zinc acetate solution and on the ZnO nanorod top plane shape.