Low-dimensional ZnO nanocrystals with controlled size, aspect ratio, and oxygen defects (e.g., type and concentration) are successfully prepared through simple solvothermal and thermal treatment methods. The structure of the as-synthesized samples is characterized by XRD, N2 physical adsorption, TEM, and IR and XPS spectra. The results show that the aspect ratio and size of the as-synthesized ZnO nanocrystals increase with increasing [OH-]/[Zn2+]; the morphology evolves from nanorod to nanoparticle with an increase in the annealing temperature; the BET surface areas of the corresponding samples decrease during these processes, respectively; and different oxygen defects, which are likely to be oxygen vacancy (Vo**) and interstitial oxygen (Oi''), are formed in our experiments accordingly. With evolution of the structure, IR absorption bands and visible photoluminescence emission peaks of the synthesized ZnO nanocrystals shift and split, which is ascribed to the change of oxygen defects. In addition, it is found that the photocatalytic activity of the synthesized ZnO nanocrystals is mainly dependent on the type and concentration of oxygen defects. The relationship of structure-property and the possible photocatalytic mechanism are discussed in detail.

Ag/ZnO heterostructure nanocatalysts with Ag content of 1 wt % are successfully prepared through three different simple methods, where chemical reduction and photolysis reaction are adopted to fabricate the heterostructure. The dispersity of Ag clusters and/or nanoparticles in Ag/ZnO nanocatalyst is investigated by EDX mapping and XPS techniques. The experimental results show that deposition-precipitation is an efficient method to synthesize Ag/ZnO nanocatalyst with highly dispersed Ag clusters and/or nanoparticles; the photocatalytic activity of Ag/ZnO photocatalysts mainly depends on the dispersity of metallic Ag in Ag/ZnO nanocatalyst; the higher the dispersity of metallic Ag in Ag/ZnO nanocatalyst is, the higher the photocatalytic activity of Ag/ZnO photocatalyst should be. In addition, it is also found that the dispersity of Ag/ZnO photocatalyst in the dye solution is another key factor for liquid-phase photocatalysis due to the UV-light utilizing efficiency. The higher the UV-light utilizing efficiency is, the higher the photocatalytic activity of Ag/ZnO heterostructure photocatalyst should be. IntroductionSemiconductor-based heterostructures with desired compositions and/or morphologies can modulate the properties of materials and find potential applications in biomedicine, photocatalysis, and nanodevices. 1-12 Stimulated by these applications, significant advances have been made to design various kinds of semiconductor-based heterostructures, such as core/ shell and anisotropic (e.g., dimer/trimer-type and hierarchical composite materials) heterostructures 13-17 in recent years. So far, metal/semiconductor is one of the most popular heterostructures and has been extensively studied because of its excellent catalytic activity. For example, recently, Ag/ZnO heterostructure photocatalyst with high catalytic activity has attracted much research attention. [18][19][20][21] However, the relationship between the structure and the photocatalytic property of Ag/ ZnO heterostructure photocatalyst is still not clear. Considering the relatively high price of Ag species and the promising application of Ag/ZnO photocatalyst, we expect to find an effective method to decrease its cost (i.e., decrease the Ag content of Ag/ZnO photocatalyst) and understand the effect of the dispersity of Ag clusters and/or nanoparticles in Ag/ZnO photocatalyst on its photocatalytic performance.It is well-known that material properties are determined by structure, such as size, morphology, pore, defect, and composition. 18,[22][23][24][25] With the photocatalytic performance of semiconductor-based heterostructure photocatalyst as an example, it is mainly dependent on the concentration of heterostructure interface and defect which can increase the separation efficiency of photogenerated electron-hole pairs. As an example, in our previous study, 18 it is found that Ag nanoparticles and oxygen

A network-structured SnO(2)/ZnO heterojunction nanocatalyst with high photocatalytic activity was successfully synthesized through a simple two-step solvothermal method. The as-synthesized samples are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, N(2) physical adsorption, and UV-vis spectroscopy. The results show that the SnO(2)/ZnO sample with a molar ratio of Sn/Zn = 1 is a mesoporous composite material composed of SnO(2) and ZnO. The photocatalytic activity of SnO(2)/ZnO heterojunction nanocatalysts for the degradation of methyl orange is much higher than those of solvothermally synthesized SnO(2) and ZnO samples, which can be attributed to the SnO(2)-ZnO heterojunction, the pore structure, and higher Brunauer-Emmett-Teller (BET) surface area of the sample: (1) The SnO(2)-ZnO heterojunction improves the separation of photogenerated electron-hole pairs due to the potential energy differences between SnO(2) and ZnO, thus enhancing the photocatalytic activity. (2) The SnO(2)/ZnO sample might possess more surface reaction sites and adsorb and transport more dye molecules due to the higher BET surface area and many pore channels, also leading to higher photocatalytic activity.