Various Facet Tunable ZnO Crystals by a Scalable Solvothermal Synthesis and Their Facet-Dependent Photocatalytic Activities

The facet-dependent photocatalytic performance of ZnO is still controversial, for the reason that ZnO samples with different high energy facets are hard to prepare. In this paper, three kinds of ZnO with different facet exposures, including {0001}, {101̅1}, and {101̅0} facets, were prepared by a scalable solvothermal method without using any crystal seeds, environmentally harmful chemicals, or severe reaction conditions. The morphologies of ZnO were gradually varied from prism to polyhedron with the increase of ethylene glycol volume fraction. Meanwhile, the predominant exposed facets changed from {101̅0} to {101̅1}. Increasing the volume fraction of ethylene glycol in the mixture solution further, the ZnO spheres formed, where the {0001} facet is predominantly exposed. The formation mechanism for different ZnO geometric structures and their facet-dependent photocatalytic performances were explored in detail, which indicates that the photocatalytic performance is dependent on the crystal facet exposures in the order {0001} > {101̅1} > {101̅0}. Efforts were made to explain the facet-dependent photocatalytic activities basing on the related X-ray photoelectron spectroscopy and atomic stacking model of various exposed surfaces.