ZnO nanostructures with divergent morphologies were synthesized by a facile chemical approach using various solvents and reducing agents. The synthesized nanostructures were characterized by XRD, electron microscopic techniques and fluorescence spectroscopy. The microstructural analysis shows that different morphologies of ZnO can be formed when suitable reducing agents (RAs) and solvents are used with variation in the molar ratio (β) of zinc precursor to RAs. The morphologies observed are spindles, flowers, nanoassemblies, rods and hexagonal hollow tubes. The size of spindle-shaped ZnO nanostructures varies from 1 to 5 μm, and nanoassemblies are of around 150 ± 20 nm. Each nanoassembly is the aggregation of individual nanoparticles of sizes around 4–5 nm. The optical study shows that these ZnO nanostructures have various defect concentrations and surface properties. Furthermore, the alterations and transformations in the physical and chemical properties of ZnO nanostructures significantly influenced the photo-catalytic degradation of methylene blue (MB) dye under solar irradiation. A complete degradation of MB is observed within 130 and 60 min when treated with ZnO of suitable morphology under UV and solar light radiation. This variation in time may be attributed to the availability of higher specific surface area, large amount of defects and anisotropy in morphology. © 2017, Springer Science+Business Media, LLC.