Weakened negative effect of Au/TiO2 photocatalytic activity by CdS quantum dots deposited under UV-vis light illumination at different intensity ratios
Herein, we demonstrate experimentally the coexistence of photocatalytic dual opposite roles of Au nanoparticles in a UV-vis light irradiated Au/TiO2 system. We have investigated that the photocatalytic performance curves of Au/TiO2 and CdS/Au/TiO2 for degradation of methylene blue (MB) all present a V-shape with different radiation power ratios. However, through the comparison of photocatalytic activities of Au/TiO2 and CdS/Au/TiO2 by statistics and mathematical simulation, we propose qualitatively that the deposition of CdS used as a photosensitizer could extend the Au/TiO2 light absorption range and weaken the negative effect of Au/TiO2. Compared with Au/TiO2, it is proven indirectly that the photo-excited electrons of CdS/Au/TiO2 transfer from CdS to Au, and then to TiO2. Furthermore, we discuss the photocatalytic dual opposite roles of Au nanoparticles between CdS and TiO2, the positive effect includes localized surface plasmon resonance (LSPR) and Schottky barrier (SB), and the negative effect is that Au nanoparticles can be used as a new charge-carrier recombination center. In addition, we have analyzed that the dual opposite relationship of Au/TiO2 under the irradiation of mixed-light could be regulated by changing the intensity ratio of visible to UV light as well.