Abstract: ZnO nanoparticles were prepared by calcining the precursor, zinc carbonate hydroxide,and Pd/ZnO and Ag/ZnO composite nanoparticles with the noble metal content of 0.5％(mass fraction) were obtained by photoreduction method. The as-prepared samples were also characterized by the XRD，TEM，XPS and SPS techniques, respectively. The results showed that the deposited noble metal of both Pd and Ag existed as the form of atomic clusters,and the possible reasons of forming the atomic clusters of noble metal on the surface of ZnO nanoparticles were primarily discussed. The intensity of SPS responses of ZnO nanoparticle remarkably decreased by depositing the appropriate noble metal on its surface. Moreover, Pd/ZnO and Ag/ZnO composite nanoparticles exhibited higher photocatalytic activity than ZnO nanoparticles in the experiment of photocatalytic oxidation of gas phase n-heptane. The essential reasons why the photocatalytic activity of ZnO nanoparticles improved by depositing noble metal Pd or Ag on its surface were also further discussed. In addition, the point was put forward that the photocatalytic activity of nanoparticle could be primarily evaluated by its SPS response, i.e., the weaker the SPS responseis, the higher the photoactivity.

Key words: ZnO, Composite nanoparticles, SPS, XPS, Noble metal, Photocatalytic activity