Radiative properties of hedgehog-like ZnO-Au composite particles with applications to photocatalysis

The recently proposed hedgehog-like ZnO particles (HPs) exhibit unusual dispersion behavior in fluids, which after being deposited with Au nanoparticles show great potential in the application of photocatalysis in both the ultraviolet and visible spectral range. Nevertheless, the radiative properties of hedgehog-like particles that largely determine the photocatalysis activity are not well understood. In this paper, models of hedgehog-like ZnO-Au composite particles (HP-Au) were built, and the discrete dipole approximation was applied to investigate their radiative properties in the spectral range from 0.3 to 0.8 µm. It is found that the absorption cross section of HPs increases notably with increasing number of ZnO nanorods in the spectral range from 0.3 to 0.4 µm, which can be five times that of the coated sphere for HPs having 300 nanorods. The absorption cross section of HP-Au increases with increasing amount of Au nanoparticles in the visible spectral range, but maintains at about 5 µm2 at the resonant wavelength of Au particles for Au to Zn mass concentration ratio larger than 14%. In addition, for Au to Zn mass concentration ratio below 9%, the peak absorption cross section of the deposited Au nanoparticles is larger than that of the independent one with the largest enhancement ratio being larger than 1.5. However, the light absorption by ZnO nanorods is not enhanced by the deposited Au nanoparticles. Having the same amount of the deposited Au nanoparticles, the absorption cross section of HP-Au increases with increasing particle size. In terms of light absorption, HP-Au with a larger number of lanky ZnO nanorods that are sparsely deposited with Au nanoparticles for an Au to Zn mass concentration ratio of about 9% are preferred for the application of photocatlysis.