Figure 1 SEM images, XRD patterns, and UV–vis Y-27632 price absorption spectra of ZnO, ZnO-H, and ZnO-A. SEM images of ( a ) ZnO, ( b ) ZnO-H, and ( c ) ZnO-A. XRD patterns ( d ) and UV–vis absorption spectra ( e ) of ZnO, ZnO-H, and ZnO-A. Figure 2a,b,c shows the cross-sectional SEM images of ZnO@Ag, ZnO-H@Ag, and ZnO-A@Ag. For ZnO@Ag, Ag nanoparticles tended to deposit onto the top of nanorods. A similar phenomenon has been observed and could be explained as follows [36, 52]: Because of the electronegativity difference between Zn and O, there were electric fields forming within ZnO nanorods whose top and bottom were related to the
lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO), respectively. When ZnO nanorods were illuminated by UV this website light, the electrons tend to be excited from the bottom to the top and thus the top of nanorods always accumulated more electrons, which could reduce silver ions
to form silver nanoparticles easily. For ZnO-H@Ag, Ag nanoparticles deposited uniformly on the top, side, and bottom of the ZnO nanorods with hydrogen treatment. This could be explained by two reasons: (1) after hydrogen treatment, interstitial hydrogen could incorporate into the bond connecting Zn and O and thus changed the electrostatic potential crossing nanorods, which further affected the way electrons moved under UV light illumination and therefore electrons were everywhere instead of staying at the top of nanorods [52]; (2) after hydrogen treatment, oxygen vacancies would increase and thus become the electron capturers to prevent electron–hole recombination, selleck chemical which helped the formation of much more Ag nanoparticles [48]. For ZnO-A@Ag, the formation of many Ag nanoparticles led to the destruction of one-dimensional
structure of ZnO-A. This might be due to the formation of oxygen interstitials after air treatment, which became the hole capturers, prevented the electron–hole recombination, and thus enhanced the excess formation of silver nanoparticles. Moreover, considering that the original ZnO crystalline Carbohydrate already had oxygen, the crystalline of ZnO nanorods might change after air treatment [53, 54]. The EDX analysis revealed that the atomic percentages of silver in the ZnO@Ag, ZnO-H@Ag, and ZnO-A@Ag were 1.28, 3.73, and 8.56, respectively. Obviously, the Ag content of ZnO-A@Ag was the maximum, in agreement with the above observation. In addition, the XRD patterns of ZnO@Ag, ZnO-H@Ag, and ZnO-A@Ag were shown in Figure 2d. As compared to Figure 1d, an additional peak for the (111) plane of silver (fcc) around the scattering angle of 38° was observed for ZnO-A@Ag. This peak was weak or almost invisible for ZnO-H@Ag and ZnO@Ag, respectively, because of the low Ag content. Figure 2e shows the absorption spectra of ZnO@Ag, ZnO-H@Ag, and ZnO-A@Ag. It was obvious that their absorption in the visible light region was increased as compared to Figure 1e.