Time-dependent control of phase and morphology transformation of porous ZnO hollow microspheres by a facile one-step solution route

Porous ZnO hollow microspheres with a ZnO crystalline phase of PDF # 21-1486 have been prepared by a simple one-step solution route using the trisodium citrate as a shape-directing agent. FESEM, FT-IR, TEM and XRD were used to characterize the samples. Series of experiments showed the reaction time has a prominent impact on the phase and morphology transformation. At a point of the controlling growth time, porous ZnO hollow microspheres with average diameter of 2-3 μm and hole-opening diameter of ∼0.5 μm were obtained which exhibited a high surface area (117.36 m² g^-1) and a large pore volume (0.50 cm³ g^-1). On the basis of experiment results, a possible growth mechanism of as-synthesized porous ZnO hollow microspheres was concluded to be a two-step process: the zinc citrate complexion was preferentially formed, and then the dissolution of zinc citrate complexion and the formation of ZnO crystal occurred simultaneously, which associated with the special role of the citrate anion on oriented growth.