Nanocone Decorated ZnO Microspheres Exposing the (0001) Plane and Enhanced Photocatalytic Properties

ZnO spherical particles exposing only the (0001) planes are prepared by an established solvothermal method using a water–ethylene glycol (EG) mix as a solvent. It is found that poorly crystalline nanoparticles form first, followed by their aggregation into microspheres consisting of crystallites embedded in EG and precursor molecules/ions. The grown up nanocrystallites and nanocones in the microspheres are all radially aligned. The possible formation mechanisms, in particular, the roles of water molecules, EG, and the intrinsic dipolar field of ZnO crystals, are discussed. X-ray photoelecton spectroscopy experiments indicate that the spherical particles are terminated solely by zinc atoms. Brunauer–Emmett–Teller measurements in conjunction with the degradation of methylene blue dye data demonstrate that the photocatalytic performance of the ZnO spheres depends on the growth time and is significantly improved compared to traditional ZnO nanorods. This study is a rare example which combines nanostructural characterization of ZnO particles terminated with a single (0001) plane of known Zn²⁺-polarity with their photocatalytic performance.