Efficient electrostatic self-assembly of one-dimensional CdS-Au nanocomposites with enhanced photoactivity, not the surface plasmon resonance effect

A series of CdS nanowire-Au nanocomposites (CdS NW-Au NCs) with different weight addition ratios of Au nanoparticles (NPs) are successfully synthesized by using a simple and efficient electrostatic self-assembly method at room temperature for utilizing the natural surface charge properties of the CdS NWs and Au NPs. These natural surface charge properties are dependent on the synthesis approaches. The probe reactions for photocatalytic selective reduction of nitroaromatic compounds in the aqueous phase under visible light irradiation are utilized to evaluate the photoactivity of this series of as-prepared CdS NW-Au NCs. The CdS NW-Au NCs exhibit significantly enhanced photoactivity as compared to the CdS nanowires (CdS NWs). The addition of Au NPs into the CdS NW domain enables efficient enhancement of the lifetime and transfer of photogenerated charge carriers from CdS NWs under visible light irradiation. However, the addition of excess amounts of Au NPs not only influences the penetration of light but the Au NPs also become the recombination centers, and result in decreased photoactivity. The optimal proportion of the Au NPs is proved to be 1 wt%, which indicates the synergistic effect between the CdS NWs and Au NPs. In addition, the surface plasmon resonance (SPR) effect of Au NPs is proved to not play an efficient role in the reaction and the possible photocatalytic reaction mechanism is proposed. It is hoped that this work could aid in the fabrication of 1-D semiconductor-metal nanocomposites by using such a simple and efficient electrostatic self-assembly strategy. In addition, it is also expected to enrich and supplement their application as visible light photocatalysts toward selective organic transformations through our investigation.