Experimental study of the radiative properties of hedgehog-like ZnO–Au composite particles

The hedgehog-like ZnO particles (HPs)and ZnO–Au composite particles (HP-Au)show great potential in the application of photocatalysis, due to their special nanostructure and unusual dispersion behavior in fluids. To improve the efficiency of photocatalysis, one needs to analyze and optimize the radiative transfer of nanofluids containing HPs and HP-Au. Therefore, knowledge of the radiative properties of HPs and HP-Au is of great significance. In this work, the radiative properties of HPs and HP-Au are experimentally measured in the visible spectral range, and the effect of the deposited Au nanoparticles on the radiative properties of HP-Au is investigated. The extinction cross section is obtained from the normal-normal transmittance of particle water suspensions by the improved transmission method. The absorption cross section and the asymmetry parameter are retrieved from the measured normal-hemispherical transmittance and reflectance. It is found that the extinction cross sections of HPs and HP-Au range from 9 to 11 µm², and peak at the wavelengths of about 380 and 650 nm due to the strong scattering ability of the particles. The deposited Au nanoparticles decrease the extinction cross section of HP-Au notably in the spectral range from 500 to 800 nm. The absorption cross section of HP-Au is enhanced by Au nanoparticles, which can be more than two times that of HPs. The absorption cross section of HP-Au peaks at the wavelength of about 520 nm due to the localized plasmon resonance of Au nanoparticles, which can reach 2.2 µm². The asymmetry parameters of both HPs and HP-Au increase rapidly with increasing wavelength in the spectral range from 400 to 600 nm, but for wavelength larger than 600 nm their asymmetry parameters are round 0.9 and show very small spectral variation. The deposited Au nanoparticles, however, tend to decrease the asymmetry parameter of HP-Au.