Enhanced photocatalytic performance of ZnO hierarchical nanostructures synthesized via a two-temperature aqueous solution route

 Nanosheet-assembled quasi-sphere-like ZnO was synthesized by ice-water bath and reflux steps. This hierarchically nanostructured ZnO shows significantly improved photocatalytic activity compared to ZnO nanopowder, although the surface area of the former (10.56 m2 g−1) is smaller than that of the latter (17.88 m2 g−1). The improved catalytic activity may be attributable to structural differences, including morphology, surface orientation and surface defects. Furthermore, these hierarchically nanostructured ZnO catalysts were reused for six times without any loss of activity, revealing excellent stability and recyclability.