Weakened negative effect of Au/TiO₂ photocatalytic activity by CdS quantum dots deposited under UV-vis light illumination at different intensity ratios

Abstract

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.