b S Supporting Information
' INTRODUCTIONZnO, an IIÀVI semiconductor with noncentrosymmetric wurtzite crystal structure, a direct band gap of 3.37 eV, and a large excitation binding energy of 60 meV, has been extensively investigated because of its potential applications in piezoelectric devices, transistors, photodiodes, and photocatalysis. 1À5 The unique antibacterial function of ZnO nanostructures both in the dark and under solar irradiation has also attracted great interest. 6,7 In the field of photocatalysis, ZnO is usually believed to be an alternative photocatalyst material to TiO 2 , since they have similar band gaps and similar photocatalytic mechanisms. 4,5 In addition, it was reported in several works that ZnO exhibited better activity than TiO 2 for the photocatalytic degradation of environmental pollutants, especially for the decomposition of dyes under visible irradiation. 8À10 The structure of nanomaterial, including morphology, particle size, and two-dimensional and three-dimensional architectures, can play important roles in determining the electrical, optical, and catalytic properties. A large volume of work have been done to elucidate the structureÀproperty relationship in heterogeneous catalysis and to provide useful information for the design and building of efficient nanostructured catalysts. The morphology, particle size, crystal orientation, crystallinity, and oxygen defects are some factors that influence the photocatalytic performance and stability of ZnO photocatalysts. ZnO nanostructure with different three-dimensional architectures, such as microscale rods, tubes, plates, porous hollow microspheres, and flowerlike hierarchical micro/nanoarchitecture, were fabricated by chemical vapor deposition, thermal evaporation, and
