Polymer-mediated shape-selective synthesis of ZnO nanostructures using a single-step aqueous approach

ZnO nanostructures of diverse morphologies such as nanowires, nanoneedles, nanorods, flower-like, and square-shaped have been successfully synthesized by a facile one-step aqueous based chemical approach. The fabrication method is simple, reproducible, quick, economical, and environmentally benign. The method to achieve considerable control over shape comprises two important parameters, i.e. concentration control of precursors, and applying polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG), respectively, as capping agents during the synthesis. A precise and systematic control over the concentration of the precursor leads to different geometries of ZnO nanostructures. Apart from the shape control, we also found that the PVP renders a tight control over the aspect ratio from 1 to 10 with respect to the amount (20 to 2 wt%) of PVP. The variation of polymer concentration in the reaction media controls the density of homogeneous nucleation and the crystal growth along the c-axis. The addition of PEG confines the nanowire diameter to similar to 70 nm and the length to similar to 5 mu m. The nanowires, nanorods, nanoflowers and nanodisks are crystalline in nature with wurtzite structure and hexagonal symmetry. Using photoluminescence (PL) and a physical property measurement system (PPMS), we demonstrate that the room-temperature ferromagnetic behavior in these nanostructures possibly originates from the defects present in the sample.