Weak plasmonic photocatalysis in unsupported colloidal gold nanorods

Abstract

Metal-semiconductor plasmonic nanosystems have the ability to extract photocarriers generated on colloidal gold nanoparticles efficiently through the Schottky junction. This process leads to effective visible light photocatalysis. However, due to the short lifespan of plasmon carriers, plasmonic loss occurs before extraction by the semiconductor and transfer to the adsorbent. We aim to investigate the direct transfer of plasmonic energy to adsorbed organic pollutants in visible light photocatalysis using unsupported colloidal gold nanorods (Au NRs). Our decision to use gold nanorods is based on their exceptional ability to harness a greater amount of visible light through their longitudinal surface plasmon resonance (LSPR) at 765 nm and transverse surface plasmon resonance (TSPR) band at 521 nm. Additionally, we conducted experiments to evaluate the photocatalytic capabilities under specific wavelengths, such as blue (405 nm), green (532 nm), and red (660 nm) lasers, to gain a better understanding of the -d-sp interband transition and the role of surface plasmon in photocatalysis. Surprisingly, unsupported Au NRs showed only weak plasmonic photocatalysis under all these excitations. With the help of supporting characterization tools, we observed that without semiconductor support, the photoexcited carriers over Au nanorods are not well separated, resulting in reduced photocatalysis.